# Question about pressurised CO2 and water disturbance



## amateurfishkeeper

So I'm just wondering about this new CO2 set up I'm using. Can anyone clarify this doubt I have. If I have a spray bar returning water into the tank from an external filter is it true that it shouldn't create any water disturbance on the surface of the water? In other words, should I be angling the returned water into the water under the surface so that the surface of the water is completely still? If there is disturbance will it mean that I'm driving off the CO2 that is being added by the pressurised system? And if that's the case and I'm not using any type of airstone, does it mean that I'm only relying on oxygen for the fish from the plants? I've lost a ram and six discus so far since adding the CO2 system so I'm a bit worried that this foray into CO2 is incompatible with keep fish. It would be useful to know about the CO2 / fish / oxygen balance if anyone can help. Thanks a lot!


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## ajm83

ardjuna did a good post about this here.








			
				ardjuna said:
			
		

> Without surface rippling your CO2 levels can increase up to some dangerous levels later at the light cycle (up to 80 ppm in my case). When you add rippling, your CO2 level will be somewhat lower, but at the same time more stable and constant during the whole photoperiod (40 ppm).
> 
> Also if you use for example 1 bps, the increase of CO2 concentration will be slower (more shallow) then in case you use 3 bps → in that case the increase will be steeper (like on the picture).
> 
> So what you want is:
> 1) More bps for quick increase of CO2 level to the desired level (for example, at 1 bps your CO2 gets to 30 ppm after 4 hours, while at 3 bps you achieve the same level in 2 hours).
> 2) Surface rippling for maintaining the uniform/stable/balanced CO2 level during the whole photoperiod.
> 
> PS: As you can see from the picture, aeration (using air stones) is not as effective as surface rippling.


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## Julian

Long story short, you need surface agitation to disperse CO2 else it will build up and kill everything. Then you need to add enough CO2 so that you can maintain it at 30ppm.

Just raise your spray bar/lilly pipe until you have some surface agitation, then adjust your CO2 accordingly.


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## Jose

Julian said:


> Long story short, you need surface agitation to disperse CO2 else it will build up and kill everything. Then you need to add enough CO2 so that you can maintain it at 30ppm.
> 
> Just raise your spray bar/lilly pipe until you have some surface agitation, then adjust your CO2 accordingly.



I agree with this, though i have to say its not the only way out there. Others like ADA and many famous aquascapers go for no surface agitation. But they do aerate the tank at night. Its harder to get your co2 constant this way and it normally keeps climbing through the photoperiod. I believe this is how they can get away with aparently adding quite little co2. There is also the filter variable to complicate things further , i.e if it degasses co2  and adds O2.


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## Andy Thurston

Jose said:


> I agree with this, though i have to say its not the only way out there. Others like ADA and many famous aquascapers go for no surface agitation. But they do aerate the tank at night. Its harder to get your co2 constant this way and it normally keeps climbing through the photoperiod. I believe this is how they can get away with aparently adding quite little co2. There is also the filter variable to complicate things further , i.e if it degasses co2  and adds O2.


decent regulator and needle valve solves this climbing problem.
also some ADA style tanks (no surface agitation) have an airstone running at night


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## Jose

Big clown said:


> decent regulator and needle valve solves this climbing problem.



I dont think this is totally true. Even with a good needle valve the co2 will keep climbing (through the photoperiod) if offgassing is not strong enough. Its more about CO2 gradient, imput of co2 and output.Basically both methods will level off at some point. But w/o surface movement the "equilibrium" will be reached after a long time (maybe two days sometimes), yet if there is some surface ripple the stability will be reached sooner (T. Barr recommends around 40 minutes if your diffusion method is good enough). Look at the graphs shown and youll see that w/o surface movement there is a tendency to level off but one photoperiod is not enough time. Also other things have a huge impact w/o ripple like surface scum.

But I dont think this is of any help for people starting with co2. As I said follow the first advices and keep some surface ripple.


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## amateurfishkeeper

Thanks for the responses!

I'm new to using CO2 and I'm trying to learn more as I'm going along. I don't have a PhD in botany or biochemistry or anything like that so you'll have to forgive my ignorance. I haven't memorised the genome sequences of plants etc .. you get the picture lol.

So far my observations have been that the use of Co2 has killed some fish and that's undoubtedly my fault. So I've tried to lower the amount of CO2 going into the tank. I pay attention to what the drop checker is telling me etc. I pay a lot of attention to what the fish are telling me. This is my first week of using EI and I've got massive flow in the tank which looks very well circulated - fast flowing hillstream etc. I assume the EI dosing is of some benefit but awaiting results on that . I'm trying to pick up on best practice from people who seem to know what they are talking about but also trying to develop my own instincts based on observation and experience. So I'll keep the water disturbance going in combination with closer control of the amount of CO2 going into the tank. I did have very vigorous plant growth before using CO2 but not in all species. Some just wouldn't develop at all in line with what people say about certain species. I guess it was the failure of these early planted species to grow that got me into the idea of CO2 use in the first place. So I guess it's all about finding that sweet spot or combination of factors that just somehow works. It's not about spending massive amounts of cash I guess but finding what is right for your tank. I appreciate everyone's input!!


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## Jose

amateurfishkeeper said:


> Thanks for the responses!
> 
> I'm new to using CO2 and I'm trying to learn more as I'm going along. I don't have a PhD in botany or biochemistry or anything like that so you'll have to forgive my ignorance. I haven't memorised the genome sequences of plants etc .. you get the picture lol.
> 
> So far my observations have been that the use of Co2 has killed some fish and that's undoubtedly my fault. So I've tried to lower the amount of CO2 going into the tank. I pay attention to what the drop checker is telling me etc. I pay a lot of attention to what the fish are telling me. This is my first week of using EI and I've got massive flow in the tank which looks very well circulated - fast flowing hillstream etc. I assume the EI dosing is of some benefit but awaiting results on that . I'm trying to pick up on best practice from people who seem to know what they are talking about but also trying to develop my own instincts based on observation and experience. So I'll keep the water disturbance going in combination with closer control of the amount of CO2 going into the tank. I did have very vigorous plant growth before using CO2 but not in all species. Some just wouldn't develop at all in line with what people say about certain species. I guess it was the failure of these early planted species to grow that got me into the idea of CO2 use in the first place. So I guess it's all about finding that sweet spot or combination of factors that just somehow works. It's not about spending massive amounts of cash I guess but finding what is right for your tank. I appreciate everyone's input!!




I would get a cheap (£10?) pH pen from ebay or whatever you can afford and monitor co2 via pH. Leave it hanging from your tank. You are aiming for a 1 unit pH drop which is aprox equivalent to 30 ppms of co2 no matter what water you have. This is an almost instant read whilst your drop checker takes at least an hour. Its also more accurate IMO. Dont worry about the chemistry, its all been put down in simple words already.


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## amateurfishkeeper

Thanks Jose - a great idea but sorry what does 'aiming for a 1 unit PH drop' mean?


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## Julian

If your pH is 7.8, when your lights come on your pH needs to be 6.8 to give you 30ppm of co2.


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## amateurfishkeeper

Forgive me ignorance also but if the PH pen gives me a PH reading how does that correlate to CO2 levels? Is there a table to calculate it?


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## amateurfishkeeper

Sorry you answered the question. Cheers!!


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## JamieB

Is there a good way to get surface disturbance without upsetting low flow fish, for example bettas? I use a sponge over my output and it does disturb the water surface but no where near the amount I'd imagine is required...


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## Jose

amateurfishkeeper said:


> Thanks Jose - a great idea but sorry what does 'aiming for a 1 unit PH drop' mean?



Good question.

Normally people have their co2 on a timer so  that its off at night and turns on an hour/or two before lights turn on. You should measure pH in the morning after all the co2 has escaped from the tank (you need goo aeration at night for all the co2 to "evaporate"). Lets say this measures a pH of 7.5 in the morning. Then you start adding co2 and after a couple of hours your pH should be around 6.5 (at this point lights turn on) and ideally it would stay there for the rest of the photoperiod. So like this example:

12:00 (pH=7.5) ->CO2 turns on
14:00 (pH=6.5)-> Lights turn on
.
.
.
20:00 Turn CO2 off
21:00 Turn lights off

You should take pH measurement every time you can and make sure there is a 1 unit pH "drop" through the photoperiod.


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## Jose

amateurfishkeeper said:


> Forgive me ignorance also but if the PH pen gives me a PH reading how does that correlate to CO2 levels? Is there a table to calculate it?


 Yes. the table is the pH Kh table.
http://www.barrreport.com/forum/barr-report/co2-enrichment/11862-co2-ph-kh-table

But the kH is independent here.


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## amateurfishkeeper

OK I see. The 'drop' refers to the change in the PH over time. By the way, is that example schedule the one you use? I have a timer and have the Co2 coming on one hour before the lights come on at 8am. The CO2 goes off an hour before the lights go out at 4pm (8 hour continual photoperiod). Is that the right kind of approach or am I making some kind of terrible mistake? Perhaps I need the lights to come on later like in your example?


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## Jose

amateurfishkeeper said:


> OK I see. The 'drop' refers to the change in the PH over time. By the way, is that example schedule the one you use? I have a timer and have the Co2 coming on one hour before the lights come on at 8am. The CO2 goes off an hour before the lights go out at 4pm (8 hour continual photoperiod). Is that the right kind of approach or am I making some kind of terrible mistake? Perhaps I need the lights to come on later like in your example?



It could be that you need your lights to come on later but I dont know until you measure your pH at different times. I would keep a photoperiod at first of around 6 hours, 7 tops.


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## 5678

Some interesting information in this thread. 

My water is quite hard with a KH of ~15/16 (and PH of 7.9/8.0) if I have understood things correctly, this will mask the PH drop even with the desired level of co2? 

From looking at that table I should only be getting a PH drop to around 7.3 rather than the full 1PH that gets mentioned by default? If that is correct, what colour would that translate to in a drop checker?


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## ian_m

If your water is pH of 8 then after two hours of CO2 hopefully a pH of 7 should be about 30ppm CO2 (it won't see below). A drop of one unit pH regardless of initial KH value.

Clearly this is approximate as there is clearly something else in your water adding to KH and/or altering pH, as reading at the end of the table in Toms link, 16KH water with no CO2 will have a pH of greater than 8.6 and yours isn't.

At 30ppm the drop checker should be green, however with your water and 1pH drop, I doubt it will be as green, maybe in 20ppm region as there is something else in your water affecting pH/KH.

See drop checkers here. I highly recommend the JBL one, shown below, as easy peasy to read the colour against the white strip, unlike the stupid breakable, but cool look, but a b**ger to read glass drop shaped ones.
http://www.ukaps.org/index.php?page=co2-measurement-using-a-drop-checker

The great advantage a drop checker has is it is isolated from the tank water and only reads the gas level in the water regardless of pH, salt levels and other contaminants of your tank water. Disadvantage is can take an hour or more to read, meanwhile you have gassed your fish.


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## Jose

5678 said:


> From looking at that table I should only be getting a PH drop to around 7.3 rather than the full 1PH that gets mentioned by default? If that is correct, what colour would that translate to in a drop checker?


There are a few things going on here.



5678 said:


> From looking at that table I should only be getting a PH drop to around 7.3 rather than the full 1PH that gets mentioned by default?



Do a search for this topic its not a simple one. But in the end your kH measurement has errors, thats just how they are, because they measure "alkalinity" as a whole not only kh. So if you use your kH to determine your co2 then you will always have less co2 than you expect. Its the same if you use the kH from your water supplier, in the sense that it changes during the year. This is why we take out the kH variable. It has been found that a pH drop of 1/1.2 normally correlates with 30 ppms of co2 independent of your water hardness. It doesnt even matter if you have an acid in the water because this will affect the initial ph but not the absolute "ph drop".This can be proven with the table if you could know your co2 ppm at the equilibrium with air. This is hard to grab at first. Always look at your fish for any sign of distress and change co2 very slowly.



5678 said:


> If that is correct, what colour would that translate to in a drop checker?



This is the problem with drop checkers that the coulour changes are very subtle. So from 15 to 30 ppm you might not be able to tell the difference. Plus it tells you the co2 there was 3 hours before plus co2 bubbles could influence the reading etc etc.


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## Jose

ian_m said:


> Clearly this is approximate as there is clearly something else in your water adding to KH and/or altering pH, as reading at the end of the table in Toms link, 16KH water with no CO2 will have a pH of greater than 8.6 and yours isn't.



What is in the water will not affect the pH drop very much even if it affects the starting pH. So dont worry if you dont see the starting pH matching that on the table for "your" kH. 1 pH drop will still be aprox=30 ppm of co2. This is the same as saying forget about your kH because you really dont know it.


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## aaron.c

I am having similar problems/worries.  I know I need surface agitation, but how much should we be aiming for?

I have heard it needs to not break the surface, but what does this actually mean - can it be very vigorous as long as it doesn't cause bubbles on the top.

I.e - in this video I shot a while back - https://www.dropbox.com/s/19sshhmkpl2i8x5/Video 13-03-2015 18 48 18.mov?dl=0

The outlets from the spray bar are just under the surface.


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## Jose

aaron.c said:


> I am having similar problems/worries. I know I need surface agitation, but how much should we be aiming for?
> 
> I have heard it needs to not break the surface, but what does this actually mean - can it be very vigorous as long as it doesn't cause bubbles on the top.
> 
> I.e - in this video I shot a while back - https://www.dropbox.com/s/19sshhmkpl2i8x5/Video 13-03-2015 18 48 18.mov?dl=0
> 
> The outlets from the spray bar are just under the surface.



There is no easy way to know if your surface ripple is right. You just set it at a certain ammount (eye balling) and then via pH set your co2.


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## 5678

Jose/Ian, thank you for the detailed replies. 

Am I correct then in understanding I should still see an approx 1ph drop in my tank regardless of the KH then? To help me with the setup, am I OK to use a PH test kit at regular intervals and just ignore the drop checker at first?

I'm thinking that if I turn it off for 24/36 hours and then take my baseline ph again, then turn the co2 back on and start measuring at hourly intervals this might give me the best information to work with?


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## aaron.c

Jose said:


> There is no easy way to know if your surface ripple is right. You just set it at a certain ammount (eye balling) and then via pH set your co2.


I know that the two are relaetd, but I wondered if there was a concensus of the amount of surgace agitation that we should aim for, then I can adjust CO2 accordingly 

Thanks Jose


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## Julian

Think about it, there's no way to measure surface agitation. You can't count the amount of ripples per second...


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## Jose

5678 said:


> Am I correct then in understanding I should still see an approx 1ph drop in my tank regardless of the KH then?



Yes.


5678 said:


> To help me with the setup, am I OK to use a PH test kit at regular intervals and just ignore the drop checker at first?


Yes. But I wouldnt use a ph test kit. I would use a ph pen. Even cheap ones are very good.


5678 said:


> I'm thinking that if I turn it off for 24/36 hours and then take my baseline ph again, then turn the co2 back on and start measuring at hourly intervals this might give me the best information to work with?


Yes. But you shouldnt really need to have it off for that long. 8-12 hours should be enough, but you do need surface agitation at least for that one night, so that you find out your starting pH.


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## Jose

aaron.c said:


> I know that the two are relaetd, but I wondered if there was a concensus of the amount of surgace agitation that we should aim for, then I can adjust CO2 accordingly


To be honest I dont know what  is a good ammount. But as long as you see your surface moving slightly and no surface scum formation (this is the main point). For example if you do like ADA and you aerate at night, then any surface film that forms during the day will go away and water will be cristal clear in the morning. This way youll need less ripple during photoperiod. Also in the beginning of a tank setup surface scum is most probably going to be there IME, so maybe then you need more.


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## 5678

Jose said:


> Yes.
> 
> Yes. But I wouldnt use a ph test kit. I would use a ph pen. Even cheap ones are very good.
> 
> Yes. But you shouldnt really need to have it off for that long. 8 hours should be enough, but you do need surface agitation at least for that one night, so that you find out your starting pH.



I have a cheap one that I bought from ebay so will use that. I've only had it a week since calibrating it so hopefully it isn't too far out yet!

I have my co2 going off at 2030 and lights off at 2130, I have a spray bar approx 1" below the surface and what I'd call substantial surface agitation. However the drop checker is not going back to blue in that time (ends up green). To be fair, I think I am massively overdosing my co2 at present though and reaching far higher than 30ppm as it's been yellow most days (and as I mentioned in my introductions post, I've managed to gas all my fish already  hence trying to get it right now before I restock)


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## aaron.c

Julian said:


> Think about it, there's no way to measure surface agitation. You can't count the amount of ripples per second...


No appreciate it's impossible to measure, so we can only make crude guestimations by looking at videos of best practice (as used by others) and try to match it as best we can.

If I can get a best practice for agitation and follow it, I can remove that as a variable, and manage CO2, via injection rate

Tricky business this


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## Julian

aaron.c said:


> No appreciate it's impossible to measure, so we can only make crude guestimations by looking at videos of best practice (as used by others) and try to match it as best we can.
> 
> If I can get a best practice for agitation and follow it, I can remove that as a variable, and manage CO2, via injection rate
> 
> Tricky business this


You're over thinking it in this regard. As long as your surface ripples at least half way across the width of the tank, you're doing it right.


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## aaron.c

Thanks Julian


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## Jose

5678 said:


> To be fair, I think I am massively overdosing my co2 at present though and reaching far higher than 30ppm as it's been yellow most days (and as I mentioned in my introductions post, I've managed to gas all my fish already  hence trying to get it right now before I restock)


main reason to use that ph pen. But leave hanging in the tank otherwise it might take a long time to stabilize the reading everytime. Also I havent seen anyone gas their fish with a 1 unit pH drop and some surface movement.



aaron.c said:


> Tricky business this


Very!


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## 5678

Jose said:


> main reason to use that ph pen. But leave hanging in the tank otherwise it might take a long time to stabilize the reading everytime. Also I havent seen anyone gas their fish with a 1 unit pH drop and some surface movement.



Hence my thinking that I am putting way too much in at the moment. It was a stupid mistake and I was (still am!) very upset with myself for it. They had been fine for the previous 1.5 days and we popped out for a few hours on Sunday afternoon and I came home to see that I had killed them all (2 x GBRs, 6 x Harlequins, 2 x Corydoras)


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## Jose

5678 said:


> Hence my thinking that I am putting way too much in at the moment. It was a stupid mistake and I was (still am!) very upset with myself for it. They had been fine for the previous 1.5 days and we popped out for a few hours on Sunday afternoon and I came home to see that I had killed them all (2 x GBRs, 6 x Harlequins, 2 x Corydoras)


Learn from your mistakes. CO2 is risky specially in the beginning. So dont put expensive fish in. Change co2 very slowly and always count BPS and pH drop. I dont really understand it when people put discus in a co2 high tech tank. Im definately not at that level of skill.


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## 5678

Jose said:


> Learn from your mistakes. CO2 is risky specially in the beginning. So dont put expensive fish in. Change co2 very slowly and always count BPS and pH drop.



Thanks Jose. I am trying to do just that. I foolishly rushed into it and have paid the price. 

I have some more kit turning up today (more robust bubble counter, extra check valve, external heater) which I will fit tonight and adjust my system to a consistent 0.5bps. 
I will measure the PH first thing tomorrow morning. and then measure it when I get home from work approx 3 hours after it has come on. I'll then adjust based on what I find.


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## ian_m

aaron.c said:


> I know that the two are related, but I wondered if there was a concensus of the amount of surgace agitation that we should aim for, then I can adjust CO2 accordingly


You will just have to play and see.

If I angle my spray bar down/horizontal I get a green/yellow drop checker and if slightly above horizontal I get a green drop checker.

Be very careful about angling the spray bar up to far, especially on an open top tank. Many people have come home to an empty tank and wet carpet, where the water level has dropped a bit allowing a jet of water to squirt out the tank, lowering the level even more until you get loads of jets emptying your tank onto the floor...nice.


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## Julian

ian_m said:


> Be very careful about angling the spray bar up to far, especially on an open top tank. Many people have come home to an empty tank and wet carpet, where the water level has dropped a bit allowing a jet of water to squirt out the tank, lowering the level even more until you get loads of jets emptying your tank onto the floor...nice.



One day I'm going to go on holiday and forget about my water level dropping. The jets that come out of my spray bar reach half way across the room..!


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## aaron.c

That would not be ideal would it.


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## Andy Thurston

Jose said:


> I would get a cheap (£10?) pH pen from ebay or whatever you can afford and monitor co2 via pH. Leave it hanging from your tank. You are aiming for a 1 unit pH drop which is aprox equivalent to 30 ppms of co2 no matter what water you have. This is an almost instant read whilst your drop checker takes at least an hour. Its also more accurate IMO. Dont worry about the chemistry, its all been put down in simple words already.


only a sucker trusts these ph pens and they fail much quicker when you leave them in the tank, been there done that. binned it after a couple of months
http://www.ebay.co.uk/itm/like/3712...3=1&ff11=ICEP3.0.0-L&ff12=67&ff13=80&ff14=108
even if they are calibrated every time you use them


Jose said:


> (T. Barr recommends around 40 minutes if your diffusion method is good enough).


Have you managed to get your tank algae free on toms recommendations yet?
tom also has wet/dry filters to keep o2 levels up and injects co2 into a needle wheel return pump which helps lower ph faster.
decent quality gear makes it much easier to get co2 just right, why else would tom barr use high end dual stage regs and high quality metering valves. his metering valve probably costs more than most peoples entire co2 system.


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## 5678

To update on my tank, got home and the drop checker is a nice shade of light green. Not sure on the bubble rate for today though as the counter leaked. 

Cheap ph pen is telling me I'm at ph 8.0 though! I'll try my api test kit and see what that says. 

Fitted my new bubble counter and have it at 0.8bps. 

I'm going to watch how the ph pen and drop checker behave over night and then let it run tomorrow before making any more adjustments. 

Big clown, what sort of money do you need to spend for a reliable ph measuring device?


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## Edward Courtney

Hi, this is a good thread, thanks for kicking it off amateurfishkeeper.
What I'm getting here is that measuring ph with an electronic device is much more reliable than using a drop checker for measuring CO2, is that the general consensus? If that's the case then great, I like reliable accuracy and it's one less fiddly glass thingy hanging in my display!
I've used a ph controller on my reef system but that was for running a calcium reactor and balancing KH which is quite a different kettle of fish (excuse the pun). 
When I reboot my system having converted it to high tech planted I'll be running it with a sump where the CO2 will be injected. I'm thinking about using a 70mm CO2 Bazooka positioned right in front of the intake for the return pump, the thought process being that the CO2 bubbles will be drawn into the impeller and diffused efficiently into the water column, like a CO2 reactor, before the water is returned to the display. The return pipe is at a depth of about 100mm below the water surface in the display but there will be a fair bit of surface agitation as the return pump will be running at 2000LPH and I'll have a Vortech MP10 in the display as well. Display is 100cm x 40cm x 50cm, 200L. Does that sound like a good plan to you guys?


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## ian_m

No the drop checker is much much better indicator if CO2 levels as it is isolated from all the pH affecting gunk in your tank water. pH pens are affected by being from Ebay/China, needing calibrating and other salts in the water causing false reading. Problem with drop checker is the delay of an hour or two before its colour settles.


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## 5678

Thanks again Ian. The drop checker has stayed at green all evening so I will see where it is in the morning and then allow it to run again tomorrow with no more adjustments. 

If I get home tomorrow and it's the same green I may up the bps ever so slightly and see how it is the next day.


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## Jose

Big clown said:


> only a sucker trusts these ph pens and they fail much quicker when you leave them in the tank, been there done that. binned it after a couple of months
> http://www.ebay.co.uk/itm/like/3712...3=1&ff11=ICEP3.0.0-L&ff12=67&ff13=80&ff14=108
> even if they are calibrated every time you use them



Ive been using mine for over a year. It barely needs calibrating and it goes off maybe 0.1 ph units every month or so. But obviously batteries have to be changed quite often.



Big clown said:


> Have you managed to get your tank algae free on toms recommendations yet?


Ive got a pretty algae free Tank yes. And I can say 98% of what Ive applied CO2-wise is from T. Barr. Even if I get algae is because Im just lazy or many other reasons.



Big clown said:


> tom also has wet/dry filters to keep o2 levels up and injects co2 into a needle wheel return pump which helps lower ph faster.
> decent quality gear makes it much easier to get co2 just right, why else would tom barr use high end dual stage regs and high quality metering valves. his metering valve probably costs more than most peoples entire co2 system.


Yeap agree. Its not possible for everyone to achieve but you should try to get as near to that as you can if you have high light. My co2 takes 2-3 hours to get a 1 unit ph drop.



Big clown said:


> decent quality gear makes it much easier to get co2 just right, why else would tom barr use high end dual stage regs and high quality metering valves. his metering valve probably costs more than most peoples entire co2 system.


Its not only about cost. You can get the same results with things from co2art. You jut have to know how.


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## Jose

ian_m said:


> No the drop checker is much much better indicator if CO2 levels as it is isolated from all the pH affecting gunk in your tank water. pH pens are affected by being from Ebay/China, needing calibrating and other salts in the water causing false reading. Problem with drop checker is the delay of an hour or two before its colour settles.



I cant believe people still recommend dropcheckers. But hey up to everyone to decide for themselves. What is better? To use a two colour indicator (dropchecker) or a 0.1 pH unit indicator that has been calibrated? You could say a pH pen is 5 times at least more accurate and that without getting into the time delay factor of the d.c

People should buy the most expensive pH pen they can afford. Im just saying that Ive used a cheap one for a year and still use it. It works for me.


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## Julian

Jose said:


> Ive been using mine for over a year. It barely needs calibrating and it goes off maybe 0.1 ph units every month or so. But obviously batteries have to be changed quite often.
> 
> 
> Ive got a pretty algae free Tank yes. And I can say 98% of what Ive applied CO2-wise is from T. Barr. Even if I get algae is because Im just lazy or many other reasons.
> 
> 
> Yeap agree. Its not possible for everyone to achieve but you should try to get as near to that as you can if you have high light. My co2 takes 2-3 hours to get a 1 unit ph drop.
> 
> 
> Its not only about cost. You can get the same results with things from co2art. You jut have to know how.



How do you keep the yellow pH controller mounted onto the tank?


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## Jose

Julian said:


> How do you keep the yellow pH controller mounted onto the tank?



Its not very neat. I use a pair of  twizzers tied with cello tape to my ph pen and hang it on the rim of the tank. If you can afford something better go for it please. Ive recommended this one cause its as cheap as a d.c.


----------



## Julian

Jose said:


> Its not very neat. I use a pair of  twizzers tied with cello tape to my ph pen and hang it on the rim of the tank. If you can afford something better go for it please.



And do you leave it turned on all the time? Why not just put the cap back on and only use it when needed? Just curious.


----------



## Jose

Julian said:


> And do you leave it turned on all the time? Why not just put the cap back on and only use it when needed? Just curious.


Because it takes sime time to stabilize once you put it in from fresh. Maybe 3-5minutes sometimes. This is why people think they dont work. They are just slower specially if battery is not fresh. Yes I keep it on most of the time. Once you know a ballpark of how many BPS you need then you can toss it and follow a D.C only if you feel the urge but Ive tried this and I doubt Im ever going back to a D.C.

Another option is to get a really good KH test kit which might be around £100+pH unit.


----------



## 5678

Hmmm, odd one this morning. 

Drop checker was still green, but the PH pen had shown an increase of 1 ph. This is confusing. 

Even if the PH pen is not calibrated correctly, a relative rise of 1 ph is still a rise, no? There is significant surface agitation (I have an e701 at full speed and the spray bar 1" below the surface in a 50l tank) so it should have gone back to blue?


----------



## Jose

5678 said:


> Even if the PH pen is not calibrated correctly, a relative rise of 1 ph is still a rise, no?


Yes, unless the pH pen is really messed up or you have some kind of electric current in your tank which I dont know the name for in english.


----------



## Jose

5678 said:


> Drop checker was still green, but the PH pen had shown an increase of 1 ph. This is confusing.
> 
> Even if the PH pen is not calibrated correctly, a relative rise of 1 ph is still a rise, no? There is significant surface agitation (I have an e701 at full speed and the spray bar 1" below the surface in a 50l tank) so it should have gone back to blue?



Which do you reckon is right/more right?


----------



## 5678

Jose said:


> Which do you reckon is right/more right?



I'm not too sure! 

I lean towards believing the PH pen more, but then I cannot get my head around how the drop checker, which is supposed to be isolated from external influences, does not tally up?


----------



## ian_m

5678 said:


> I lean towards believing the PH pen more, but then I cannot get my head around how the drop checker, which is supposed to be isolated from external influences, does not tally up?


Provided you haven't contaminated the drop checker fluid it will be right and pH pen wrong. The absolute value of pH is being affected something else in the water. You are all heading down the Matrix of misleading numbers game. Hey my latest gadget reads 6.8 (or what ever) so something must be wrong, what must I do.....

If your water is soft the pH pen will be hopelessly wrong, I think you need at least 4KH before you should even consider a reading. Oh you don't know your KH so how can you trust your pH reading.....If you claim you know you KH from where ?? Most hobby test kits are really alkalinity test kits oh which rely on pH to read KH....see the circular Matrix of numbers.....

Your drop checker is indicating there is still residual CO2 in the water, fine no problem with that, you have gone to great effort getting CO2 in there, not a problem. My drop checker often stay green next morning depending on spray bar angle, air pump not being on, age of drop checker fluid etc etc. No problem. I take the drop checker out and within 1/2 an hour it is dark blue.

The only thing you can rely on with the pH pen is the rough differential change in pH of 1 unit drop. Some people need 1.5 pH drop or greater to get their drop checkers green. In a tank you cannot correlate the KH value with absolute value of pH as there is so much else going on in the tank. Luckily these things cause you to under read pH values (acidic) thus you get a 1 pH drop with only 20ppm CO2, so you under dose CO2 rather than overdose and kill your fish.

So in summary, aim for 1 pH drop due to CO2 at lights on as a good start, you will probably be under 30ppm CO2, so safe start there. Use this in conjunction with drop checker, plant health and fish activity to gauge CO2 levels. Don't rely on the numbers too much, use the numbers in conjunction with what you see and work on that.


----------



## Jose

ian_m said:


> Provided you haven't contaminated the drop checker fluid it will be right and pH pen wrong. The absolute value of pH is being affected something else in the water. You are all heading down the Matrix of misleading numbers game. Hey my latest gadget reads 6.8 (or what ever) so something must be wrong, what must I do.....



Which Matrix is real. The colours one or the numbers one. Most of the d.c fluids Ive owned never went back to theyr original colour. But a pH pen you can calibrate, a d.c you just trust. That without getting into the 4dkh solution in it and wether you make them yoursel.



ian_m said:


> The absolute value of pH is being affected something else in the water.


This is true and that is why we measure "pH drop" which will not be affected (at least not a lot) by other bases and sure not by an acid in the water. Why? Well if you have a water and you add acid to it, the starting pH will change but so will the kH, yet the "pH drop" will stay quite close to being 1 (for 30 ppms). So all that changes is your starting point (pH) which you can monitor every morning anyway.



ian_m said:


> Your drop checker is indicating there is still residual CO2 in the water, fine no problem with that, you have gone to great effort getting CO2 in there, not a problem. My drop checker often stay green next morning depending on spray bar angle, air pump not being on, age of drop checker fluid etc etc. No problem. I take the drop checker out and within 1/2 an hour it is dark blue.



If he wants to find out then he should leave the water being aerated for another day, or how long do you say the residual co2 might stay in there?



ian_m said:


> The only thing you can rely on with the pH pen is the rough differential change in pH of 1 unit drop. Some people need 1.5 pH drop or greater to get their drop checkers green. In a tank you cannot correlate the KH value with absolute value of pH as there is so much else going on in the tank. Luckily these things cause you to under read pH values (acidic) thus you get a 1 pH drop with only 20ppm CO2, so you under dose CO2 rather than overdose and kill your fish.


This is your misinterpretation of the science behind it Ian. The pH drop is normally between 1 and 1.4 yes but this has got more to do with the co2 in the equilibrium (which we cant measure). But I can tell you even so its much more accurate than a d.c.



ian_m said:


> So in summary, aim for 1 pH drop due to CO2 at lights on as a good start, you will probably be under 30ppm CO2, so safe start there. Use this in conjunction with drop checker, plant health and fish activity to gauge CO2 levels. Don't rely on the numbers too much, use the numbers in conjunction with what you see and work on that.



See, one thing we agree on 100%.

Ideally and this is what T Barr recommends: Youd measure pH drop needed until you see any sign of stress on your critters. Now say that is 1.4. You now know what you should be aiming for. Youve got your refference now. If you add an acid to the water or the kh changes then you should still aim for the same ph drop but the final ph value will be different as well as the starting value.


----------



## Jose

ian_m said:


> The only thing you can rely on with the pH pen is the rough differential change in pH of 1 unit drop. Some people need 1.5 pH drop or greater to get their drop checkers green. In a tank you cannot correlate the KH value with absolute value of pH as there is so much else going on in the tank. Luckily these things cause you to under read pH values (acidic) thus you get a 1 pH drop with only 20ppm CO2, so you under dose CO2 rather than overdose and kill your fish.



This is another great thing about this method. You wont gass your fish with a 1 ph drop but you are also most probably over 20 ppm which is not bad. Then you can add more co2 to change ph 0.1 units every time. Youll never be able to do this with shades of green and yellow. So you are more likely to gass fish with a d.c.


----------



## 5678

Some excellent advice from you both that I greatly appreciate. 

I'm learning more with each post you guys make and think I have a solid set of information to work from. 

One thing I may try, is to leave my tank without co2 until the drop checker goes blue and get my relative ph reading at that point.


----------



## 5678

Looks like some element of success yesterday. 

I recalibrated the PH pen (for what its worth!) and measured the following:
0640 7.6 DC Green
1425 7.4 DC Blue/Green (co2 had been on for approx 60 mins)
(lights on at 1430)
1745 6.9 DC Green (also swapped the JBL DC for a pretty glass one! upped the bps a fraction.)
1930 6.7 DC Green
(co2 off at 2030)
2210 7.3 DC Dark Green

Then this morning:
0650 7.8 DC Blue

So it seems I'm not too far off with things now? 

Annoyingly I broke the diffuser last night so I've turned co2 and lights off for today. 

I changed the angle of my spray bar ever so slightly to increase surface agitation which seems to have worked with gassing off over night. I am still seeing all plants swaying though. 

I'm planning to run this for a few days to try and make sure I get the DC green and the PH around 6.8/6.7 by lights on by adjusting the co2 on time.


----------



## Jose

5678 said:


> 1745 6.9 DC Green (also swapped the JBL DC for a pretty glass one! upped the bps a fraction.)
> 1930 6.7 DC Green



See? A 0.2 pH change and I doubt you can see the change in colour of the d.c. All it takes to gas your fish is a 0.1 ph change and even less. You cant really know if youre anywhere near without measuring pH.

I think youre doing well by using both methods, because its all about the confidence and experience on what works.


----------



## 5678

Yes, this is teaching me that measuring PH (even relative rather than actual) is better for me than a DC. I can see myself buying a PH controller quite soon. 

I've also got the advantage of not having any fauna so minimal risk. Once I've got it stable then I will add some fish on a day I am in to watch them as the co2 kicks in and ramps up then adjust as necessary.


----------



## Jose

5678 said:


> I've also got the advantage of not having any fauna so minimal risk. Once I've got it stable then I will add some fish on a day I am in to watch them as the co2 kicks in and ramps up then adjust as necessary.



Good idea. I am keeping  a fish-less tank at the moment because I had many problems with a fluctuating BPS due to a bad needle valve. That is another biggie, the regulator. But even if you have a cheap one it can be made to perform great with a flow controller.

Here is someone using a pH controller if its of any interes:

http://www.ukaps.org/forum/threads/mountain-view.35570/#post-404150


----------



## 5678

I'll take a look at that tonight. No pictures load on the work network! 

I have the co2art dual stage solenoid regulator. It wasn't their top one, but they suggested to to me as being better than most.


----------



## Jose

5678 said:


> I have the co2art dual stage solenoid regulator. It wasn't their top one, but they suggested to to me as being better than most.



Ive got the cheap one stage one with the solenoid. Its impossible to get a constant BPS in my case. Im sure a double stage one is better though.


----------



## 5678

Lets hope so! I've not had much luck so far.


----------



## Jose

5678 said:


> Lets hope so! I've not had much luck so far.


If co2 is not constant take a look at this:

http://www.co2art.co.uk/collections/splitters-manifolds-valves/products/advance-co2-flow-controller

Im still trying it out.


----------



## 5678

So you just open the needle valve fully then fit that inline before the bubble counter?


----------



## Jose

5678 said:


> So you just open the needle valve fully then fit that inline before the bubble counter?



Thats what Ive done. But didnt really open the needlevalve all the way, but pretty sure thats what you should do. Its important to fix the little knob with the thread its got, once flow is set.


----------



## dw1305

Hi all,





Edward Courtney said:


> What I'm getting here is that measuring ph with an electronic device is much more reliable than using a drop checker for measuring CO2, is that the general consensus? If that's the case then great, I like reliable accuracy and it's one less fiddly glass thingy hanging in my display! I've used a ph controller on my reef system but that was for running a calcium reactor and balancing KH which is quite a different kettle of fish


This bit is quite important, if you have very heavily buffered salt rich water (sea water is carbonate buffered and ~53,000 microS) then any pH meter will give you a fairly accurate measurement. As you move towards pure H2O (an electrical insulator) pH becomes both a less meaningful measurement, and much more difficult to measure.

You can't extrapolate from a buffered system (like Lake Tanganyika) to a much less buffered situation like the Amazon basin black (and clear) water rivers and lakes.

These problems come about because pH is a ratio, and "pH7" just means you have an equivalent number of H+ ion donors ("acids") and H+ ion acceptors ("bases"). It doesn't matter what that number is it could be 1:1, 10:10, 100,000:100,000 as long as it is a balanced equation.

This is also why pH can never be stable in very soft water, very small changes in the relative proportions of weak acids (like H2CO3) and weak bases (like O2)  cause large changes in pH. 





ian_m said:


> Provided you haven't contaminated the drop checker fluid it will be right and pH pen wrong.


 This is also why "Ian_m" is right, pH meters are high maintenance bits of kit that need to be regularly calibrated (with pH buffers) and have their electrodes stored in a  KCl solution etc.

They aren't "plug and play". If you are willing to spend a couple of hundred pounds on a pH meter/electrode combination, and have the time to buffer it before each use, it will give you an accurate and repeatable reading.

Drop checkers are accurate (<"read this thread">), and use the fact that carbonic acid (H2CO3) and bi-carbonate (HCO3-) are the weak acid and weak base pair in carbonate buffering.

Calcium carbonate is insoluble in water, but in water with carbonates present the small amount of CO2 (that goes into solution as H2CO3) is in equilibrium with the HCO3- to give a stable value of ~pH8 at atmospheric CO2 levels (400ppm CO2) and standard barometric pressure (1013mb).

When we add CO2 above atmospheric levels we drive the H2CO3 ~ HCO3- equilibrium towards H2CO3. We know that pH is a ratio, and that an acid is defined as a H+ ion donor and we've added extra H+ (from H2CO3), so the pH falls. How much the pH falls depends upon the reserve of carbonate buffering, we usually measure this as "dKH".

If we have a narrow range pH indicator ("bromothymol blue"), a solution made to contain 4dKH solution ("4dKH solution"), a drop checker with an air gap and a chart with experimentally derived  CO2 levels for a range of pH values at a known carbonate hardness (below) it is a pretty robust system.



 
cheers Darrel


----------



## 5678

Wow, thats a detailed reply, and above my ability to comprehend in one go! 

Darrel, you sound very competent on this topic, does my approach sound correct? Ultimately, I appreciate that I need to have my DC blue in the morning and Green (and stable green) when lights come on. I am using the PH pen as supplementary information to look at the relative drop. 

I know I have hard water (how hard, I'm not sure, I only have basic test kits which I know are not accurate.) and that it has a naturally high PH (again, not sure exactly.) Based on this and the tables, I am not expecting to see a full PH drop, but I am still expecting my DC to go between blue and green once the correct amount of co2 is present in the system.


----------



## ian_m

Jose said:


> Here is someone using a pH controller if its of any interes:





dw1305 said:


> This is also why "Ian_m" is right, pH meters are high maintenance bits of kit that need to be regularly calibrated (with pH buffers) and have their electrodes stored in a KCl solution etc. They aren't "plug and play".


This is why most people (there are exceptions, like the link you posted) using CO2 controllers either end up gassing their fish or adding no CO2 and growing algae. CO2 controllers (actually measuring pH) are high maintenance bits of kit where going out of calibration causes issues. Much better to not use CO2 controller and get your CO2 rate (bps) consistent every day and observe levels with drop checker and/or pH pen if you feel you need numbers rather than colours .


----------



## Jose

I agree with the veterans in here but will just add a couple of opinions.

1) If you look at most cases of people gassing their fish they are normally using a d.c. Most everyone Ive seen having algae issues use a d.c.
2) Normally we dont have KH under 4 in our planted tanks. Obviously this is a drawback of the pH  method, but they all have drawbacks, and I think d.c. have more.
3) Also having high or low light makes a difference. If you want to have more control over your co2 a pH meter is a must. Otherwise, do you know someone other than T. Barr who adds more co2 to his tank without gassing his fish while monitoring with a d.c? Sorry but Im afraid none of us do. Even the best aquascapers in here. They use a d.c because thats what they learned with and they just adapt the light to need less co2, and theyve also learned to eyeball it etc.

Its all been said in that link Darrel added.


----------



## dw1305

Hi all, 





5678 said:


> Wow, thats a detailed reply, and above my ability to comprehend in one go!


Water chemistry, and particularly buffering and pH, is quite a difficult area, which is why a lot of comment on the web isn't as informed as it should be. I'm not a CO2 user, mainly because I can find quite enough ways to kill my fish without adding another one. 





5678 said:


> Ultimately, I appreciate that I need to have my DC blue in the morning and Green (and stable green) when lights come on. I am using the PH pen as supplementary information to look at the relative drop.


 Yes, you will just get less pH drop in harder water. 





5678 said:


> I know I have hard water (how hard, I'm not sure, I only have basic test kits which I know are not accurate.) and that it has a naturally high PH (again, not sure exactly.)


 You should be able to get values from your water supplier.

The only hardness value you need to know accurately is that the drop checker solution is 4dKH.

Because the drop checker has an air gap, only CO2 will effect the pH.

Your added CO2 will continually out-gas (until dissolved CO2 levels equilibrate with atmospheric levels).

The CO2 that out gases into the drop checker will effect the pH (and the colour of the pH indicator), nothing else will. When you stop adding CO2, it will re-equilibrate with atmospheric CO2 levels  and your drop checker solution will revert to ~pH8.

The lag in colour change occurs because gases are moving in and out of the drop checker via diffusion and the rate of diffusion will depend
upon the diffusion gradients between the tank water, air  gap and 4dKH solution.

The steepness of diffusion gradients will depend upon the area of the gas exchange surface. This is why people have air pumps they turn on when the gas is off.  A larger gas exchange surface will out-gas the CO2 more quickly.

cheers Darrel


----------



## Jose

dw1305 said:


> Yes, you will just get less pH drop in harder water.



This is something I am very interested in Darrel. Hope you take your time to explain it to me as always.

Harder water=higher Kh right?

*The pH kH Co2 chart shows that "pH drop" is independent of the kH *up to where Im concerned. If you do an example with two waters with different khs you will find this out. lets try:

Water 1: KH=2, Ph at the equilibrium with air=7.6(lets suppose we have 1.5 ppm of co2 and this shouldnt matter since both water will have the same rough co2 ppm in the equilibrium with air)
water 2: KH=5, Ph at the equilibrium with air=8( again lets suppose we have 1.5 ppm of co2 and this shouldnt matter since both water will have the same rough co2 ppm in the equilibrium with air)

Now lets look at the pH for both waters once we add 30 ppms of co2.
Water 1: KH=2, pH (at 30 ppms of co2)= 6.3
water 2: KH=5, (at 30 ppms of co2)=6.7

pH drop for water 1=7.6-6.3=1.3
pH drop for water 2=8-6.7=1.3

Same pH drop for two waters with different kH as to get the same co2 dissolved in them.
How can this be Darrel? Maybe the CO2 at the equilibrium with air is not the same? But then T. Barr would be wrong.

I used this chart which is more detailed but should be the same:
http://www.barrreport.com/forum/barr-report/co2-enrichment/11862-co2-ph-kh-table

I really believe here lies the core of the conflict. People say KH affects pH drop because it looks intuitive.


----------



## Marcel G

I did not verify it, but maybe it was meant to mean that to lower pH by CO2 supply in hard water you will have to add more CO2 (in volume) then to lower pH by the same value in soft water.


----------



## Jose

ardjuna said:


> I did not verify it, but maybe it was meant to mean that to lower pH by CO2 supply in hard water you will have to add more CO2 (in volume) then to lower pH by the same value in soft water.



He (T. Barr) also states that you need approx the same ammount of co2 for both waters. He states that the solubility might be slightly different but it wont make a difference at all when adding co2, at least no a measurable difference. So you are right Ardjuna probably but this will not affect the "ph drop" .


----------



## dw1305

Hi all, 





Jose said:


> This is something I am very interested in Darrel. Hope you take your time to explain it to me as always. Harder water=higher Kh right?


 The simple answer is I don't know. 





ardjuna said:


> but maybe it was meant to mean that to lower pH by CO2 supply in hard water you will have to add more CO2 (in volume) then to lower pH by the same value in soft water.


Yes, that is exactly what I had in mind.
_
"Harder water=higher Kh right?_" Intuitively that would be the reason, but as it is a buffered system I'm not sure. It wouldn't matter what dKH you started with, assuming all the hardness was via carbonates (and there weren't any acids other than H2CO3) then the pH would be ~pH8, whether it was 1 dKH or 20 dKH. Because of the small reserve of buffering at 1 dKH, you don't have to add much CO2 before you get a rapid fall  in pH. Looking at the chart once you get above 4 dKH that relationship is more linear.  I'm not a CO2 user, but there is an explanation in Ardjuna's thread <"here">. 

CO2 is a bit funny because it exists as a dissolved gas and as an acid, and carbonic acid (H2CO3) is "diprotic" - it has two H+ ions, so it has 2 disassociation constants.

All the chemistry "bits" are here, but the chemistry is beyond me: <http://lawr.ucdavis.edu/classes/ssc102/Section5.pdf>.

cheers Darrel


----------



## Jose

Thanks Darrel. I appreciate it.



dw1305 said:


> _"Harder water=higher Kh right?_" Intuitively that would be the reason, but as it is a buffered system I'm not sure. It wouldn't matter what dKH you started with, assuming all the hardness was via carbonates (and there weren't any acids other than H2CO3) then the pH would be ~pH8, whether it was 1 dKH or 20 dKH. Because of the small reserve of buffering at 1 dKH, you don't have to add much CO2 before you get a rapid fall in pH. Looking at the chart once you get above 4 dKH that relationship is more linear



Maybe the chart is not very accurate. I understand other acids/bases/buffers play a role here, but if we want to see the effects of kH then we need an experiment with only KH(carbonates/bicarbonates/ Na2CO3?) + CO2 + pure H20. This is supposedly what the pH/Kh chart is right? And in the more detailed chart it looks like no matter what KH the ph drop is the same for a certain co2 ppm and starting with the same equilibrium. I've tried with the lowest value and also with the highest. Maybe the chart is just a formula which doesnt represent reality for all khs?

I understand people might think I'm overthinking this but this makes a difference IMO.

I can just say that I've had a pH drop of 1.1 in my tank without gassing my fish, but this water is possibly all carbonates. It would be nice to show what happens in waters with other buffers in it. This tank has a high KH of around 18 possibly. And its seems Toms experience shows the pH drop varies from 1.1 to 1.4 normally. So I might be wrong but we have a range here of 0.3 ph units of unknown. Its not that much if you think you can add co2 up to a ph change of 1 without risks (well not too many anyway).

Anyways, all I can say is that it remains a matter of opinions for now.


----------



## dw1305

Hi all,
Jose I'll ask a colleague who is a chemist. But I think I've got it. 

Assuming that the _"pH drop of 1_" for ~30ppm CO2 is right, it is because it is a buffered system, and pH is a log10 scale. The drop in pH is determined only by the concentration of CO2 in the water.

In the same way a reserve of HCO3- (dKH) will maintain pH at ~pH8 at atmospheric CO2 levels, as you increase the CO2 levels you drive the equilibrium towards H2CO3 and the pH falls.

Assuming you still have a reserve of buffering then the fall in pH may appear to be linear (exponential data plotted as log10 values will form a straight line). 

I think everything starts from *the assumption that water in equilibrium with atmospheric CO2 levels contains ~3ppm CO2*. A drop of 1 pH unit is actually an increase of 10 in the ratio of H+:O-H ions, when you have a pH drop of 1 unit you have:

*3ppm x 10 (1 as log10) = 30ppm CO2.*

This is from <"The Planted Tank"> 





> But what I was saying, about the derivatives, if what hoppy was saying is correct, then that means that change in pH (Y) is a function of change in KH (X) (X change in KH results in Y change in pH). This means that the derivative of this function (dy/dx) is independent of CO2. This does not mean that the variable of pH (Y) itself is independent of CO2. If it was, then (dy/dz) would be zero, meaning that CO2 would not affect pH. So, pH has some sort of relationship with CO2 (Z) a very complex one. pH (Y) is dependent on both pH and CO2, but dy/dx and dz/dy are independent of each other.
> 
> Ok, hold on, based on what hoppy said, the equation is Z/Zo=10^(Yo-Y) which means Z=Zo[10^(Yo-Y)]
> so to calculate CO2(Z), you plug in starting ph for Yo, and current pH for Y and I guess we are assuming that the starting CO2 is 3ppm?


This also looks an understandable link <http://institutebishop.org/enviro_11.pdf>.

cheers Darrel


----------



## Jose

dw1305 said:


> Assuming that the _"pH drop of 1_" for ~30ppm CO2 is right, it is because it is a buffered system, and pH is a log10 scale. The drop in pH is determined only by the concentration of CO2 in the water.
> 
> In the same way a reserve of HCO3- (dKH) will maintain pH at ~pH8 at atmospheric CO2 levels, as you increase the CO2 levels you drive the equilibrium towards H2CO3 and the pH falls.
> 
> Assuming you still have a reserve of buffering then the fall in pH may appear to be linear (exponential data plotted as log10 values will form a straight line).
> 
> I think everything starts from *the assumption that water in equilibrium with atmospheric CO2 levels contains ~3ppm CO2*. A drop of 1 pH unit is actually an increase of 10 in the ratio of H+:O-H ions, when you have a pH drop of 1 unit you have:
> 
> *3ppm x 10 (1 as log10) = 30ppm CO2.*



See? I wouldnt have said it in a million years, even though I think I understand it cause Ive done some chemistry in the past.

So just to recap Darrel. Could we conclude that "pH drop" is independent of KH? Even if its not exactly 1 unit of ph. In other words you need the same pH drop no matter the hardness of the water. Now there are also other acids/bases. And this is another big question. Is it still the same pH drop if we add an acid that? I think it is because it will break down KH. And is it the same pH drop if we add a base? Dont know.


----------



## Jose

Jose said:


> So just to recap Darrel. Could we conclude that "pH drop" is independent of KH? Even if its not exactly 1 unit of ph. In other words you need the same pH drop no matter the hardness of the water. Now there are also other acids/bases. And this is another big question. Is it still the same pH drop if we add an acid that? I think it is because it will break down KH. And is it the same pH drop if we add a base? Dont know.



Actually this is quite easy to test and Im testing it indirectly now in my tank. Im adding H3PO4 to lower pH whilst maintaining the same BPS and difussion method. Ill find out today if the pH drop stays approx the same. Yes I know this isnt scientific but its something.


----------



## 5678

Going well for me again today it seems,

Dc was a blue/green at lights on with a 0.7ph drop. 
2.5 hours into my lighting period now and the dc is green and a full 1ph drop. It seems to be static at this point too. 

If it stays green all day then I am going to add some fish tomorrow.


----------



## 5678

Bugger, it went yellow late in the day. 

Have closed the needle valve slightly and increased surface agitation a touch. 

It's not exact I know, but what bps do people use for tanks around 50l?


----------



## Andy Thurston

1/2 - 1 bps with a jbl proflora bubble counter (big bubbles)
how late in the day did it go yellow?
If you've reduced the injection rate you might want to start injecting co2 a little earlier
you can also turn the co2 off before the end of the photoperiod, in my tank co2 goes off 3hours before lights
Its a tricky business this co2 injection


----------



## 5678

It was around 6/7pm when it went on at 12. 

After knocking it back a bit and watching it closely today, it went green around 3.30pm so I've set it to start 30 mins earlier tomorrow. 
Ph dropped from 8.1 to 7.6 which using the Barr table puts me just into green. I'm going to aim for 7.4 next time I'm home to monitor things. 

I've added fish today too so will only be making VERY small changes now.


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