# Why do we aim for 30 ppm CO2?



## John P Coates

Hi folks, 

I get the impression that 30ppm is the target CO2 concentration in planted aquaria. If what I say is correct, why is 30 ppm CO2 considered optimum?

Looking at the Tropica aquatic plants website, I see that many, if not most, plants are happy with less than 15ppm. That being so, I am inclined to aim for 15ppm in the new tank that I am setting up. But then there will be implications, some of which I've already thought of being:

1  Do I need to adjust my drop checker to 2°dH instead of 4°dH?

2  Do I need to switch CO2 off at night? 

3  My CO2 cylinder should last longer.

4  Lower CO2 should be better for the fish. 

Am I overlooking something? 

JPC


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## darren636

its a compromise
just enough for nice plant growth whilst keeping fish arive.


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## Nathaniel Whiteside

darren636 said:


> keeping fish arive.



Great Terry Tibbs accent D.


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## Vazkez

Hi,

Most tropica plants has the "15" because that's "easy" plants to keep ( do not need souch lite to grow ). More light = more CO2 uptake. How Nathaniel said 30 is satisfy amount for plants and your fish does not suffer. However all this are just numbers you should see how fish and plants doing. Anything above 30 can harm your fish...

1 sorry no idea
2 yea you should if you do not want to turn you fish tank to gass chamber and kill everything. However if you want to run it in night as well the you will need to run air pump too
3 yes that's another reason why switch it off
4 yes but it is not harmful below 30

Vaz


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## ian_m

Also bare in mind that most peoples disasters with planted tanks is with co2 levels and distribution. So 30ppm and off at night had been proved time and time again, so tread carefully.


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## Ian Holdich

And also keep your c02 consistent...I've found this probably the most important part.


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## harryH

Ian Holdich said:


> And also keep your c02 consistent...I've found this probably the most important part.




Absolutely, and probably one of the most difficult.


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## Ian Holdich

harryH said:


> Absolutely, and probably one of the most difficult.



Just don't touch the regulator! Lol


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## Aquadream

The CO2 concentration depends on the amount of light. 30 ppm is just about ideal for tanks with medium light.
I also keep my CO2 constant 3+ bps forever.


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## John P Coates

Ian Holdich said:


> And also keep your c02 consistent...I've found this probably the most important part.


Hi Ian,

Many thanks for your reply.

What do you mean by 'keep your CO2 consistent'? Does this mean that I need to ensure the CO2 ppm does not vary - is that correct? If so, how do I achieve this overnight? Should the CO2 be switched off overnight? And, if so, what about the pH swings?

JPC


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## ian_m

No, he means constant CO2 ppm during lights on time.

So you turn CO2 on say 2 hours before you lights to allow level to reach say 30ppm (green drop checker). You keep 30ppm (green drop checker) until about 1hour before lights off.

During lights off the CO2 will disperse, faster if you use an air stone, but as lights are off plants (& algae) don't make use of CO2.

Some people, especially with smaller tanks, run CO2 24/7, again constant ppm during lights on, but obviously wasting CO2 during the night.


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## Ian Holdich

Yes, once you have your c02 at a stable level, leave it at that. It should be off at night, this is why we use solenoids. Then you don't have to touch it at all.


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## John P Coates

Aquadream said:


> The CO2 concentration depends on the amount of light. 30 ppm is just about ideal for tanks with medium light.
> I also keep my CO2 constant 3+ bps forever.


Hi Aquadream,

Are you able to put a (PAR) figure on 'medium light'? My point about 30ppm CO2 is that it is twice the figure required by many plants, according to Tropica. So, if nothing else, we are subjecting our fish to twice the CO2 concentration than may be necessary. And we're wasting CO2.

I note that you don't switch your CO2 off overnight. That's what I would prefer to do.

JPC


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## harryH

John P Coates said:


> And we're wasting CO2.
> I note that you don't switch your CO2 off overnight. That's what I would prefer to do.



But surely there's no bigger waste of CO2 than to run it overnight when your plants no longer need it?


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## John P Coates

harryH said:


> But surely there's no bigger waste of CO2 than to run it overnight when your plants no longer need it?


Hello Harry,

Fair point. But, as with a lot of things, it's a question of finding the right balance, isn't it? So, if I have to waste CO2 overnight but it's better for the fish because the pH is more stable, which would I choose? That's why I'm interested in the target CO2 concentration of 30ppm. Because, overnight, the CO2 concentration will increase if not switched off and perhaps attain unsafe levels. So, we have to switch the CO2 off using a solenoid valve. But if the target concentration of CO2 during the day was, say, 15ppm, we may be able to leave CO2 on overnight with no risk to the fish and pH may be sufficiently stable. I don't know the answer to this, which is why I started this thread. From what I have read, it just seems to me that the choice of 30ppm CO2 is somewhat on the high side.

JPC


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## Vazkez

Hi,

I know this does not answer your question, however if you wnat ot keep just the "easy" plant you better go low tech (withoud CO2) and saveyourself lots of trouble


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## harryH

Hello John, well we are all learning and I can only relate my own method.

I have always attempted to get my CO2 to a maximum acceptable level during daylight hours, once there I aim to keep that level by, as Ian says above leaving the regulator alone.

There are of course so many factors which is why tanks differ in their requirements one to another and why I remarked keeping a consistent level is not always easy. Number of plants, lighting, flow distribution etc but as plants give off CO2 at night, oxygen levels can be greatly reduced. I would never think of lowering the CO2 during the day so that I can run it overnight. Better to aim for the mythical 30ppm during the day and switch off at night, using the method of having CO2 come on an hour or even 2 hours prior to lights on and going off before lights out.

If you have a spray bar or power head causing a ripple effect of the water surface, oxygen levels can be maintained at night.

I have to admit I used to always have my CO2 on 24/7 years ago but do feel I have more control over it these days via a solenoid plus it's greater economy is a big consideration especially on large set-ups.

Harry.


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## ian_m

http://www.practicalfishkeeping.co.uk/content.php?sid=5264


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## John P Coates

harryH said:


> Hello John, well we are all learning and I can only relate my own method.
> 
> I have always attempted to get my CO2 to a maximum acceptable level during daylight hours, once there I aim to keep that level by, as Ian says above leaving the regulator alone.
> 
> There are of course so many factors which is why tanks differ in their requirements one to another and why I remarked keeping a consistent level is not always easy. Number of plants, lighting, flow distribution etc but as plants give off CO2 at night, oxygen levels can be greatly reduced. I would never think of lowering the CO2 during the day so that I can run it overnight. Better to aim for the mythical 30ppm during the day and switch off at night, using the method of having CO2 come on an hour or even 2 hours prior to lights on and going off before lights out.
> 
> If you have a spray bar or power head causing a ripple effect of the water surface, oxygen levels can be maintained at night.
> 
> I have to admit I used to always have my CO2 on 24/7 years ago but do feel I have more control over it these days via a solenoid plus it's greater economy is a big consideration especially on large set-ups.
> 
> Harry.


Hi Harry,

Thanks for detailing your method of controlling CO2. Your feedback is very useful.

John C.[DOUBLEPOST=1396451857][/DOUBLEPOST]





ian_m said:


> http://www.practicalfishkeeping.co.uk/content.php?sid=5264


Hi Ian,

Thanks for the link to the excellent article. It makes for very interesting reading and it addresses many of the issues that were whizzing around in my mind.

John C.


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## John P Coates

Vazkez said:


> Hi,
> 
> I know this does not answer your question, however if you wnat ot keep just the "easy" plant you better go low tech (withoud CO2) and saveyourself lots of trouble


Hi Vaz,

On the contrary, it's no trouble at all. As a scientist, I have an enquiring mind. I like to understand exactly what's going on 'under the hood'. No stone left unturned and all that. I have no wish to stay with just the easy plants. The thing is that I had a four year break from aquarium fishkeeping and now I can't get enough of it. So, if there's something I don't understand, I ask. I've successfully grown (with CO2) quite a few aquarium plants before. I wouldn't dream of keeping fish without live plants - they are beautiful and an important part of the aquatic ecosystem.

John C.


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## Lee Sweeting

Hi john! Have you checked your ph profile? This is probably the best way to check if you are injecting enough co2. 


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## Aquadream

John P Coates said:


> Hi Aquadream,
> 
> Are you able to put a (PAR) figure on 'medium light'? My point about 30ppm CO2 is that it is twice the figure required by many plants, according to Tropica. So, if nothing else, we are subjecting our fish to twice the CO2 concentration than may be necessary. And we're wasting CO2.
> 
> I note that you don't switch your CO2 off overnight. That's what I would prefer to do.
> 
> JPC


Medium light would be anything near 50 PAR.
The fish is not concern about the amount of CO2 unless is in toxic levels. Also waisting CO2 is relative and depends on how desperate you are to get your plants to look really good. CO2 is cheap enough.
I have about 250 CRS in my tank and they are not much concerned about the CO2 either since I see they are breeding well.
I found turning on and off the CO2 to be more of a problem than constant good levels, because of the PH shifts that are far more stressful IMO than some extra CO2.
Besides with Amazonia this days I have little choice. High CO2 or no plants.


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## John P Coates

Lee Sweeting said:


> Hi john! Have you checked your ph profile? This is probably the best way to check if you are injecting enough co2.


Hi Lee,

I haven't started injecting CO2 yet as I am still setting the tank up. My new regulator should arrive tomorrow and the first bubbles in the tank are likely to appear this coming Friday.

JPC


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## Lee Sweeting

John P Coates said:


> Hi Lee,
> 
> I haven't started injecting CO2 yet as I am still setting the tank up. My new regulator should arrive tomorrow and the first bubbles in the tank are likely to appear this coming Friday.
> 
> JPC



Ah! Sorry mate, I should have read your post properly. :-@. 

You shouldn't worry about the 30ppm number. As above, you need to inject enough co2 for healthy plant growth but not so much that you harm your fish. 

As I said check your ph profile once you are up and running. This is defiantly the best way to check how efficiently you are injecting co2. 

Looking forward to seeing the tank 




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## John P Coates

Aquadream said:


> Medium light would be anything near 50 PAR.
> The fish is not concern about the amount of CO2 unless is in toxic levels.
> I found turning on and off the CO2 to be more of a problem than constant good levels, because of the PH shifts that are far more stressful IMO than some extra CO2.


Hi Aquadream,

Thanks for the feedback. I have extracted from your original post the points above as they are of particular interest to me.

Firstly, your idea of medium light is what I had in mind.

Secondly, the toxic CO2 level for fish is what I am unsure about. For a start, it seems to be dependent on the dissolved oxygen concentration, which makes sense. It also varies from species to species. Most of the research I have found is in the field of aquaculture. Young fry may be more vulnerable to CO2 than adult fish. And so it goes on.

Finally, pH fluctuations. Presumably, this will be dependent on the KH of the aquarium water. I would expect the lower the KH, the more the pH will fluctuate. What I don't know is how much pH variation fishes are comfortable with. And it's not just the pH variation but the rate of change of pH.

JPC


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## Aquadream

PH fluctuations do not depend on the KH, but on variation of the CO2 concentration. KH is considered a relatively constant factor unless there are materials such as some rocks that can react with the CO2 injected in aquaria resulting in raise of KH.
Now what PH fluctuations the fish would be comfortable with is a difficult question to answer.
Some scientists (I am not one) would suggest some values, but IMO fish would like PH fluctuations as much as humans would like temperature or moisture fluctuations over the 24 hours period.
What they can tolerate is a different matter to which I am not competent to give an adequate answer..
I consider stable PH to be the best way.


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## Sacha

Sorry Aquadream, pH fluctuations do depend on KH. 

As an illustration, a 20 PPM increase in Co2 may lower the pH by 0.8 in low KH water, while the same in increase in Co2 may only lower the pH by 0.1 in high KH water. 

The fish don't mind the pH change as such, as it is not paired with a sudden change in TDS, so it won't shock their Osmoregulatory system. 

When people talk about fish being sensitive to pH changes, they usually mean that they are sensitive to TDS changes, which are often coupled with hardness and pH changes. 

Hope this is clear


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## John P Coates

Sacha said:


> When people talk about fish being sensitive to pH changes, they usually mean that they are sensitive to TDS changes, which are often coupled with hardness and pH changes.


Hi Sacha,

That's very interesting. I wasn't aware of that. Is it not the case, though, that pH changes can affect fish independent of TDS? I am not a fish physiologist so I'm on shaky ground here.

JPC


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## Sacha

Yes, of course changes in pH can affect fish independent of TDS, but they are much more sensitive to TDS and hardness than they are to pH. 

Fish have been found thriving in parts of the Amazon where the pH is about 6 at night, and about 2.5-3 during the day.


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## John P Coates

Sacha said:


> Yes, of course changes in pH can affect fish independent of TDS, but they are much more sensitive to TDS and hardness than they are to pH.
> 
> Fish have been found thriving in parts of the Amazon where the pH is about 6 at night, and about 2.5-3 during the day.


Hi Sacha,

Thanks for putting me straight on that.

Your last sentence is of particular interest.

JPC


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## Sacha

Indeed. I'll try and find the article I was reading and post it here.


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## John P Coates

Aquadream said:


> I consider stable PH to be the best way.


Hi Aquadream,

So, presumably you leave CO2 running overnight?

Is your CO2 set for 30ppm concentration?

May I ask - what fish do you keep?

JPC[DOUBLEPOST=1396603723][/DOUBLEPOST]





Sacha said:


> Indeed. I'll try and find the article I was reading and post it here.


That would be good to read.


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## petn

Sorry Aquadream, pH fluctuations do depend on KH. <br /><br />As an illustration, a 20 PPM increase in Co2 may lower the pH by 0.8 in low KH water, while the same in increase in Co2 may only lower the pH by 0.1 in high KH water. <br /><br />The fish don't mind the pH change as such, as it is not paired with a sudden change in TDS, so it won't shock their Osmoregulatory system. <br /><br />When people talk about fish being sensitive to pH changes, they usually mean that they are sensitive to TDS changes, which are often coupled with hardness and pH changes. <br /><br />Hope this is clear<br/>
I think aquadream is considering stable kh in a tank, which produce always the same results concerning ph decrees.so no fluctuation here!? What has been mentioned was variations in co2 concentrations while injecting and that's a bit tricky to avoid. My regulator seems to do a good job though although having a splitter for four tanks on top of it. 

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## petn

Sorry messed up here a bit with coppying the previous post,not sure how to do it on phone properly  

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## petn

http://www.ukaps.org/forum/index.php?posts/3241

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## petn

Not sure if you saw this tutorial by clif. U may find it interesting and useful as I did. 

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## Aquadream

Sacha said:


> Sorry Aquadream, pH fluctuations do depend on KH.
> 
> As an illustration, a 20 PPM increase in Co2 may lower the pH by 0.8 in low KH water, while the same in increase in Co2 may only lower the pH by 0.1 in high KH water.
> 
> The fish don't mind the pH change as such, as it is not paired with a sudden change in TDS, so it won't shock their Osmoregulatory system.
> 
> When people talk about fish being sensitive to pH changes, they usually mean that they are sensitive to TDS changes, which are often coupled with hardness and pH changes.
> 
> Hope this is clear


If KH is stable in any given aquaria then the PH fluctuations will not depend on it but on CO2 fluctuations. KH is suppose to be the buffer capacity of any aquarium and assist in keeping the PH stable, not the factor that causes PH fluctuations.
We can smart argue forever over this, but KH unstable tank is basically a recipe for disaster.
So when you make a statement against another statement remember that this is not philosophical discussion considering all possibilities, but in particular a stable aquarium.

Other wise PH fluctuation can depend on more than KH and CO2 if we get to dig too deep.

PH can change where TDS can remain constant because PH depends on CO2 and TDS does not. Also PH is related to TDS, but again TDS is suppose to be a relatively stable parameter in aquarium. TDS would not change significantly ever if we do not add fertilisers. Of course you could go onto the water evaporation, but there the answer would be simple to. Top up with RO will prevent huge changes in TDS readings. So your second statement is quite incorrect am afraid.

I would say the discussion should revolve around the basics of stable aquatic environment, not around what could happen or how many chemical possibilities are out there, because that would get on the way of the hobby.[DOUBLEPOST=1396644428][/DOUBLEPOST]





Sacha said:


> Yes, of course changes in pH can affect fish independent of TDS, but they are much more sensitive to TDS and hardness than they are to pH.
> 
> Fish have been found thriving in parts of the Amazon where the pH is about 6 at night, and about 2.5-3 during the day.


PH 6 at night and 2.5-3 during the day??? Are you sure is not the opposite. In nature CO2 will build up in aquatic environment at night not during the day. So at night PH will be lower, because during the day all plants will use up the CO2.

If TDS is stable in aquarium the fish will not be sensitive to it. So instead of getting at what the fish can be sensitive to you should be looking up for stable parameters in your tank.


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## Sacha

I didn't realise you were talking about KH in one specific tank. You simply said "pH fluctuations do not depend on the KH". Which is obviously wrong. 

Secondly, you say that my second statement is quite incorrect? In what way exactly? Are you trying to say that changes in pH caused by Co2 give the fish Osmoregulatory difficulties?


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## Sacha

Indeed, that was a mistake. It was the other way around.


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## Aquadream

John P Coates said:


> Hi Aquadream,
> 
> So, presumably you leave CO2 running overnight?
> 
> Is your CO2 set for 30ppm concentration?
> 
> May I ask - what fish do you keep?



As I said my CO2 runs forever, meaning literally forever. It never stops and it goes at rate 3-4bps.
I have about 250 CRS in the tank, no fish yet. I would refrain from fish for a while, because I want the CRS to multiply even more.[DOUBLEPOST=1396644955][/DOUBLEPOST]





Sacha said:


> I didn't realise you were talking about KH in one specific tank. You simply said "pH fluctuations do not depend on the KH". Which is obviously wrong.
> 
> Secondly, you say that my second statement is quite incorrect? In what way exactly? Are you trying to say that changes in pH caused by Co2 give the fish Osmoregulatory difficulties?


Yes if the PH changes caused by CO2 are big enough.

On the first one please get out of the chemistry class. This is an aquatic forum and we are discussing aquatic realities, not basic water chemistry.
Yes PH fluctuations does depend on KH if you want to regulate PH in this way, but in aquarium PH is not regulated in this way. In aquarium KH have to be stable and serve as a PH buffer not to contribute to PH fluctuations. Not just in one specific tank, but in all of them.


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## Sacha

"On the first one please get out of the chemistry class. This is an aquatic forum and we are discussing aquatic realities, not basic water chemistry."

There's no need to take that tone. This is an aquatic forum. By definition, water chemistry is a huge part of our hobby. It is one of the most important things we should discuss. I don't understand why you've taken issue with it. I misunderstood your post is all. It seemed like you thought that the KH and pH are completely unrelated. Obviously I was mistaken, so it's just a failure to communicate, no disagreement as such. Sorry if I've been at all confrontational


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## ceg4048

Sacha said:


> Secondly, you say that my second statement is quite incorrect? In what way exactly? Are you trying to say that changes in pH caused by Co2 give the fish Osmoregulatory difficulties?





Aquadream said:


> Yes if the PH changes caused by CO2 are big enough.



Sorry mate, this is definitely not true. There are zero osmoregulatory effects of pH changes due to CO2. Fauna will perish due to CO2 toxicity long before they are affected by pH. Carbonic acid is a very weak acid and does not produce enough free H+ to make a difference in the Na+:H+ exchange mechanism.  In any case I can have (and have done) as much of a pH drop as I want without any issues. I specifically controlled the pH drop by a combination of varying the alkalinity and varying the CO2 content until the pH exhibited extreme drops. Fish bred in this water with a pH drop of approximately 5 units (pH 7-> pH 2) which is approximately 100,000X increase in acidity. So the answer, at least as far as S.A Dwarf chiclids, common Tetras and Discus are concerned, is.....No.

Cheers,


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## Sacha

Exactly, thank you Clive.


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## Aquadream

ceg4048 said:


> Sorry mate, this is definitely not true. There are zero osmoregulatory effects of pH changes due to CO2. Fauna will perish due to CO2 toxicity long before they are affected by pH. Carbonic acid is a very weak acid and does not produce enough free H+ to make a difference in the Na+:H+ exchange mechanism.  In any case I can have (and have done) as much of a pH drop as I want without any issues. I specifically controlled the pH drop by a combination of varying the alkalinity and varying the CO2 content until the pH exhibited extreme drops. Fish bred in this water with a pH drop of approximately 5 units (pH 7-> pH 2) which is approximately 100,000X increase in acidity. So the answer, at least as far as S.A Dwarf chiclids, common Tetras and Discus are concerned, is.....No.
> 
> Cheers,


Interesting. We are talking about sudden PH fluctuations meaning as much as drop and raise as well, not just in one direction.
I have seen how fish get severely startled with this changes either hiding in corners or going top side (when CO2 is too much).
What do you think is causing that taking the TDS does not change?
I am talking about a case where the GH and KH a very high and CO2 regulates the PH down. So if CO2 stopes for any reason PH will shoot up by a lot within an hour. This is a case with many folks here that are running on tap water which is too hard and growing plants gets a bit difficult.
In one case CO2 concentration is too high, PH goes very low, but I would say it is the CO2 that's causing the trouble. So that's clear issue.
What happens if the water gets relatively fast at high PH levels let say from 5 to 15?
And then again.
What's the relevance  of TDS in this discussion if this parameter have to be stable in the first place and one does not move fish from one tank to another all day long? I have never seen TDS changes in my tanks unless I use a lot of fertilisers or let the water evaporate half way.
The only case when I had TDS changes were when I experimented with Calcite rocks in CO2 enriched aquarium and yet TDS were not changing any near fast enough to cause any problems to fish.

Yes Clive your theory is beyond question correct, but we are not moving fish all the time and aquariums are usually stable in TDS reading are they not?

If we want to say what else would get fish in osmoregulatory trouble that would be sudden shift in temperature for example and is not even TDS related, but then again it will be a man made reason, not something that would ever occur in a stable environment.

So I suggest we stop biting on the letter and get the tanks stable and then see what happens with the osmoregulatory functions of fish.


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## Sacha

Aquadream,

what you need to realise is that pH is an arbitrary and pretty meaningless measurement. It is not a measurement of anything chemically tangible, but rather it is a _mathematical procedure, _referred to as a "chemical speciation calculation". This is the function used to calculate pH:

*pH = -log aH+
*
aH+ is Hydrogen ion activity. The important thing to note here is that pH does not measure the true concentration of hydrogen. It measures the _effective _concentration. This is because it must account for the fact that other ions around the H+ ions affect their ability to participate in chemical reactions, basically changing the hydrogen ion concentration in any process that involves H+. 

pH gives a rough overview of _all _the chemicals present in a solution that contribute to acidity or alkalinity, it can't tell you anything specific.

An obvious analogy is TDS. TDS doesn't actually _mean _anything at all. TDS is (sort of) another chemical speciation calculation, insofar as it takes a reading (conductivity) and applies a mathematical function to it to obtain a different reading.

Now, what does _total dissolved solids _actually tell us? Nothing. It tells us roughly how much "solid" is dissolved in the water. But what is that solid? It might consist entirely of potassium bicarbonate, in which case the fish won't care, but it might consist entirely of chloramine and ammonia, in which case the fish will die. So two identical measurements of TDS (for argument's sake let's say 100 and 100) look identical, but can be the difference between life and death. This is because it is an overview of everything in the water.

Back to pH, it is exactly the same story. It gives a rough outline of _everything _present in the water. Let's take a theoretical swing of pH from 7.0 to 6.0. Now what has actually changed to cause this reading? The _power of hydrogen _is what has changed. What does that even mean, power of hydrogen? 

What Clive said here is the crux of the issue: 



ceg4048 said:


> Carbonic acid is a very weak acid and does not produce enough free H+ to make a difference in the Na+:H+ exchange mechanism.



The fish don't care about the pH changing. They care about whatever happened to cause the pH to change. If the pH change was caused by a significant change in the exchange mechanism, then it changes the chemical capability of the water. The water will behave in a different way in relation to other chemicals. 
If the pH change was caused by dissolution of a very weak acid, the chemical composition of the water remains basically the same. The dissolved acid is too weak to change the way in which the water behaves in relation to other chemicals. All the chemical processes/ reactions that happen will be virtually unaffected by the extra acid, and will remain pretty much the same. 

I hope I've made this clear as it's a long time since I studied this. If there are any mistakes in what I've said I'm sure Clive will pick up on them.


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## ceg4048

Aquadream said:


> Interesting. We are talking about sudden PH fluctuations meaning as much as drop and raise as well, not just in one direction.
> I have seen how fish get severely startled with this changes either hiding in corners or going top side (when CO2 is too much).
> What do you think is causing that taking the TDS does not change?


It's exactly as Sacha explains. The toxicity of CO2 has to do with the dissolved gas pressure in the water which makes it difficult for the fish to exhale. Imagine if I put a plastic bag over your head and forced you to re-breathe the air you exhale. Any living thing that consumes carbohydrates, and which burn the carbohydrates with Oxygen will always produce CO2 which has to be eliminated from their system. Within the bloodstream, the Carbonic acid that results from the tissue produced CO2 changes the pH of the blood and that acidity inhibits the Oxygen carrying ability of red blood cells. We and fish have to expel the CO2 or suffer hypoxia. High CO2 pressure in the water column pushes back against the fishes attempt to push CO2 out through the gills. 

It isn't necessary to have a large pH drop to have this happen. In high KH water, if you inject too much CO2 the fish will suffocate just as easily, but the pH drop will be very small. So the fish are responding to the high dissolved CO2, NOT to the pH drop. I think this is one of the key misunderstandings in the hobby. Fish do not care about pH or pH fluctuations, large or small. As Sacha quite rightly points out, fauna care only WHY the pH has fallen or risen. If the pH falls or rises due to a toxic agent, then they will be affected by the toxic agent, not by the pH change.

Regarding your hypothetical question of what happens if the pH rises from 5 to 15, remember that it's very difficult to separate the analysis of all the different agents in water because each factor has an effect on the other. So in order to answer this question, you'll need to specify exactly what agent caused the pH to rise. What are the initial conditions? The answer to those questions will tell you how the fish will respond. It's very difficult to raise the pH of the water from 5 to 15 except by the addition of caustic alkaline substances such as Sodium Hydroxide to the water. Sodium Hydroxide is a toxic substance and is the principle ingredient of Oven Cleaner or Drain Cleaner. So, if that is the agent being used to raise the pH then we can confidently predict that it will annihilate the fish. A more reasonable hypothetical would be to raise the pH say, from 3 to 8. That's easy to do by simply adding some salt of Carbonate, such as Sodium Bicarbonate or Potassium Bicarbonate. That will neutralize the acid in the water and will raise the alkalinity. The fish will not be affected. Another hypothetical situation is one in which the initial pH is 5 and large doses of ammonium (NH4+) is added to the water. At a pH of 5 the NH4+ <=> NH3 equilibrium is shifted mostly to the less toxic NH4+. If we now add copious amounts of any Carbonate salt to raise the pH above 7, the equilibrium will shift to the right and there will suddenly by highly toxic NH3, which will also annihilate the fish. As I mentioned before, it's very easy to drop the pH with low KH and small additions of CO2. But suppose I dropped the pH with Hydrochloric Acid and high KH water instead of using Carbonic acid? Well, yes a drop from 7 to 5 in high KH water indicates that large amounts of caustic acid has dissolved in the water and yes, this also completely annihilate the fish.

Each scenario has to be analyzed within the context of the original conditions and the agents responsible for the change of pH. To only look at the pH change itself without context is not meaningful and it is often what causes people more grief. When there is too much CO2 dissolved in the water and the fish are suffocating, we really don't care about what the pH value is. The corrective action is to change the water or to strongly aerate the water in order to remove the CO2. When this happens, the pH rises rapidly and this is never a problem. It's the correct behavior and fauna will not suffer sudden pH change trauma. Their health will immediately improve. If any negative behavior is noted under this condition, then it is a strong indicator that some other agent is in the water or that some other malady is present.

It's a very similar story with TDS. Any solid or liquid that dissolves in the water will change the TDS. If that something is toxic, like organic waste then the TDS rise will have a negative impact. If the TDS rise is due to something innocuous, like fertilizer, then there will be no ill effects.

I think you'll find that different tanks experience different rates of TDS rise/fall based on the behavior of the hobbyist. I add a lot of fertilizer throughout the week so my TDS will rise sharply. When I change the water, it will fall. People who overfeed without changing a large amount of water will experience a TDS rise that can be considered unhealthy. Some people have hardscape that dissolves, so when they add CO2 the rate of dissolution from the gravel or rocks will increase the TDS. New clay substrate will typically adsorb many components from the water and some people will see a TDS fall. After some months, the surface of the clay gets filled with the adsorbed components and the TDS fall will cease. There are so many scenarios mate, it's difficult to cover all of them with a broad general statement. We always need therefore to understand the Why of pH or TDS change.

Hope this makes sense! 

Cheers,


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## Sacha

Another great post from Clive.


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## Andy D

Sacha said:


> Another great post from Clive.



Of course! 

Yours was very informative too!


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## Aquadream

ceg4048 said:


> Each scenario has to be analyzed within the context of the original conditions and the agents responsible for the change of pH. To only look at the pH change itself without context is not meaningful and it is often what causes people more grief.


So let me spell it again then.

If PH would raise quickly from 5 to 15 what happens then?

If you would like to get the idea of this scenario please look more carefully in my last post, in context as you say.
I can see that you defend Sasha's comments vigorously because he is actually quoting your own writings.
It is to be expected from young lads that lack self identification and are looking for some recognition on forums. I don't mean to be rude. It is just a sad reality that I see on all forums. Folks picking up a smart fights to win public vote.

If you really want to comment everything in context you should do so every time.
I did not see you answering my comments in their full context, but only pulling parts that appear wrong according to your beliefs and banging the academic bible after that.

Please forgive me if I don't line up my words as you. After all I am not a scientist and do not speak or even understand your language as I am sure many others wouldn't either.

I am trying to explain things in simple terms as a hobbyist.

Alternatively I could stop posting as I did for a long time until recently just not to be on the way of the "hard science".

Please check in detail post #26 and Sasha's comment to that to get the picture in what "scientific" discussion you got involved in.

I am sure John who opened this tread got probably completely lost by now, because he never asked for smart deep answers, but for a practical advise.


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## Andy Thurston

Ph5-15 if that happened in my tank i'd think someone was adding caustic soda crystals.


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## ian_m

Thought pH only went to 14?


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## Sacha

Aquadream, I'm not even going to bother responding to that. I look forward to reading Clive's message when it eventually appears.

If the science is too complex, then let this be the message you take away from this thread:



ceg4048 said:


> Imagine if I put a plastic bag over your head and forced you to re-breathe the air you exhale.


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## Aquadream

ian_m said:


> Thought pH only went to 14?


It does indeed. It's just an over exaggerated example.


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## ceg4048

Aquadream said:


> If PH would raise quickly from 5 to 15 what happens then?


I spelled it out specifically for you in my previous response. I told you that it depends on the specific agent responsible for the pH rise. That is the context I mentioned. There are many types of acids that can drop the pH rapidly. Weak acids as well as strong ones can drop the pH quickly, but only the strong acids will cause problems. On the other side of the coin, there really are not many weak bases that can cause a dramatic pH rise that you propose. Only caustic bases can do that, and obviously these toxins would kill the fish for lots of other reasons long before any osmoregulatory issues would arise. 

I'm OK with your exaggeration because I get that you are attempting to illustrate a point, however, when you play the "what if" game you cannot just make up any scenario that comes to mind. The scenario must fit reality. Perhaps that is the difference between a simple hobbyist and a scientist. The scientist understands, to some extent, the rules of reality. That's why, in my previous post, I provided you with some alternate scenarios which were much more real world and which could actually happen. As BigClown said, 



Big clown said:


> Ph5-15 if that happened in my tank i'd think someone was adding caustic soda crystals.


And so what happens is the person adding caustic soda to the tank is committed to the Tescadero Institute for the Criminally Insane.

For a re-visit to a less psychotic scenario: 
Imagine that a large fish died unnoticed, it's body trapped and hidden in the undergrowth and decaying. The CO2 turns off at night and the pH rises from it's daytime acidic low to perhaps, above 7.0. The NH4+/NH3 equilibrium comes into play in such a scenario. So lots of times, people ask about fluctuating pH and whether it's dangerous, and the answer is, that the pH itself has no effect, however, the behavior of ammonium/ammonia will have an effect that has nothing to do with osmoregulation.

I also think that it's a bit unfair to Sacha as well as to the OP, as well as to others reading the thread. Fair enough if you don't understand the depth of the explanations, but I'm sure others have grasped at least the basics. You specifically asked the "what if?" and so, it was answered, hopefully, to the satisfaction of some. If you required additional clarification, then please advise.

Cheers,


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## Richardbunting

I have been in deep thought recently with regards to hypothetical scenarios within the planted aquarium conumdrum. To tell the truth i cleared my mind by referring to calculus.

It is as clive and sacha have said, there are just to many variables. To even differentiate the variables to give a yes/no answer on a function like what specific level or limit of co2 addition will kill fish is simply un achievable and wholly unrealistic. This "simple" statement requires deep and lengthy differentiation to reduce the variables to a point where we can define limit and max and thats on 1 aquarium as we all know there is no "ideal" situation, Otherwise we'd all have tanks like amano and plantbrain.

What am i trying to say in support of the argument? Well, know the dependant factor that will cause all of the variables associated with it. Analysis leads to complex arguments, often ending in a heated debate. But the cause of ill fish health and plant failure is almost always dependant on one fact, something that we did to aquarium X caused something variables of varying magnitudes to the Nth term.

I wish there could be a magic formula to calculate a hypothetical situation, alas it is not to be.

Relax, sit back, keep a journal, make small and infrequent adjustments and all will be fine, know your dependants, light, dosing and by means of record keeping monitor the changes. Try not to use psuedoscience to explain complex scenarios. And above all else, just enjoy yourself.

Rich


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## dw1305

Hi all, 


Sacha said:


> The fish don't care about the pH changing. They care about whatever happened to cause the pH to change. If the pH change was caused by a significant change in the exchange mechanism, then it changes the chemical capability of the water. The water will behave in a different way in relation to other chemicals. If the pH change was caused by dissolution of a very weak acid, the chemical composition of the water remains basically the same. The dissolved acid is too weak to change the way in which the water behaves in relation to other chemicals. All the chemical processes/ reactions that happen will be virtually unaffected by the extra acid, and will remain pretty much the same.


Just to say straight away that I'm not a CO2 user, as I can find quite enough ways to kill my fish without asphyxiating them, but Clive and Sacha are right in saying that changes in pH caused by changing the CO2 ~ HCO3 equilibrium don't effect the fish. 
If you have a look at this thread there is some more explanation <http://www.ukaps.org/forum/threads/co2-in-the-planted-aquarium.2270/page-2#post-295689>.

I think another problem is that people who have experience of pH in strongly buffered systems (like you might use for Rift Lake Cichlids) then extrapolate their (entirely valid) experiences to soft, low conductivity water. The problem is that in heavily buffered water falls in pH are caused by large changes in water chemistry, but as water approaches pure H2O pH becomes a less and less meaningful measurement.  

Rather than thinking of pH as an absolute measurement, I find it easier to think of it as a ratio, and rather than thinking of rather abstract H+ and O-H ions, I think of pH as "grains of sugar" in a 2 pan balance, with one pan "acids" and the other "bases". 

If the amount of sugar in both pans is balanced, the pH is pH7. You can have a grain of sugar in either pan, a sugar cube in either pan or a 2 kg bag in either pan and the pH is still pH7, as long as we are in balance. 

If you add a grain of sugar to the "acid" pan that already contains a grain of sugar, you now have twice the mass of "acids" compared to "bases" and the pH falls to a fairly low level, but we've only added one grain of sugar. If we then repeat the exercise with the balanced 2 kg bags, the added grain of sugar to the acids side now makes no practical difference to the balance and the pH remains at pH7. 

If you now think of the "acid" grain of sugar as a "H+ ion donor" and the "basic" grain of sugar as a "H+ ion acceptor", we are pretty close to understanding pH.

I hope that helps

cheers Darrel


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## sparkyweasel

Nice analogy, Darrel.


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## John P Coates

Aquadream said:


> I am sure John who opened this tread got probably completely lost by now, because he never asked for smart deep answers, but for a practical advise.


Yes, this thread has deviated somewhat from my original question. But it's all good stuff even if it gets a bit heated at times.

I have decided to go with 10 - 15ppm. Today, I made up my 2°dH KH 'reference' for my JBL CO2 drop checker. I don't know how accurate it is as I used the NT Labs test kit but it would appear that KH is difficult to measure reliably. Apparently, Hanna Instruments and La Motte make good KH test kits. The Hanna Instruments kit costs £36. Which test kits do you guys use to accurately measure KH?


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## Sacha

Salifert do a great KH kit. It's a titration test which means it's very accurate.


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## Aquadream

All my test kits are from Macherey-Nagel. Company that produces all sorts of tests for laboratories of any kind including those that control the municipality water supply.


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## Sacha

Aren't those horrifically expensive? Where do you buy them from?


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## dw1305

Hi all,


> Which test kits do you guys use to accurately measure KH?


  This one would do, <http://www.mn-net.com/StartpageWate...rdness/tabid/4768/language/en-US/Default.aspx>, but you don't really have to be able to measure dKH accurately, you just need to start with DI (de-ionised) water, it is pure H2O.

Even if you don't have access to RO, distilled or DI water, you can boil a kettle of hard water, and pour the boiling  water through a cotton handkerchief, muslin or "Brine Shrimp" sieve in to a bowl etc.

When the water boils it is de-gassed, and we already know know that CO2~ HCO3 are in equilibrium. When we boil the water all the bi-carbonates come out of solution (there is no CO2 and the equilibrium means that no CO2 = no HCO3 in solution) and form insoluble (usually calcium) carbonate "scale" (CaCO3).

Normally as the water cools CO2 would diffuse in from the atmosphere, and (as a small proportion enters solution as H2CO3), the "scale" would dissolve adding Ca++ and HCO3- ions.

But, if we filter out the "scale" there are no HCO3- ions to go back into solution as CO2 diffuses in and the pH will fall (this is why rain-water is naturally acid).    

Once we've got our carbonate free water you can then add a soluble bi-carbonate (NaHCO3 or KHCO3) to raise the alkalinity, and in most situations alkalinity is equivalent to dKH.  I won't go through the maths, but it is here: <http://www.thekrib.com/Plants/CO2/hardness-larryfrank.html>.

The bit we're interested in is adding 3.0g sodium bicarbonate (NaHCO3) to 100 litres of water will raise the alkalinity by 1 & adding 3.6g potassium bicarbonate (KHCO3) to 100 litres of water will raise the alkalinity by 1 (from
<http://www.theplantedtank.co.uk/water.htm>). So from there 12g NaHCO3 in 100 litres will be ~4dKH, or 1.2g in 10 litres of H20.  





> Salifert do a great KH kit. It's a titration test which means it's very accurate


 and now we are into the drop checker or titrimetric situation, and you can just think of a the drop checker, 4dKH solution and bromothymol blue (narrow range pH indicator) as a titrimetric method.

cheers Darrel


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