# How to test CO2 levels without dropchecker



## The Abbott (13 Sep 2010)

HI all, Is there a way of checking co2 levels without using a dropchecker? Also is there a 'base setting for a bubble counter? i.e  5 bubbles a minute, 5 bubbles a second    It's just I want to get started with my FE system but my dropchecker has not arrived yet  

Rich


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## Tom (13 Sep 2010)

There's a way by testing the kH, but it's not accurate as there are too many variables. Drop checker is the best way I know of, provided you use 4kH water in it. 

As for how many bubbles... how big is the tank?


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## The Abbott (13 Sep 2010)

its a 240l tank......


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## chrisfraser05 (13 Sep 2010)

the problem is the bubble count means nothing really.

If you used a poor diffusion method you might have about 8 bubbles per second to get 30ppm where as the same tank with a reactor might need 3 bps to get 30ppm.

there are tables online where you can compare your PH change to your KH level and it will tell you your ppm.

The best way is still go get 4dkh and blue with a drop checker. My big bottle of premixed dkh and blue plus 2 small checkers only cost me Â£14 so it was well worth it.


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## George Farmer (13 Sep 2010)

This is way I've done it -

1.  Take a sample of tank water in a test tube.
2.  Shake it vigorously for 60 secs to ensure all CO2 has been gassed off.
3.  Test the pH.  Let's say it's pH 7.6.
4.  Take another sample of tank water, at an appropriate point in time to ensure plenty of CO2 is present.
5.  Test the pH.  Let's say it's pH 6.6.

A difference in 1 pH should equate to approx. 30ppm CO2.

Less than a 1 pH difference = <30ppm CO2.
More than 1 pH difference = >30ppm CO2.


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## chrisfraser05 (13 Sep 2010)

that varies depending on the hardness of the water though doesn't it george?

I thought that if your water was say 2kh 1ph difference would be like 10 ppm and if you had water of say 16kh 1 ph would be 100ppm


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## chrisfraser05 (13 Sep 2010)

found this graph, kind of shows the relationship in a round about way.

Was hoping to find the one that shows it clearer.


http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html


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## George Farmer (13 Sep 2010)

chrisfraser05 said:
			
		

> that varies depending on the hardness of the water though doesn't it george?
> 
> I thought that if your water was say 2kh 1ph difference would be like 10 ppm and if you had water of say 16kh 1 ph would be 100ppm


Not according to my calculations 

Let's do KH 20
pH 8.3
CO2 would be around 3ppm (assuming only carbonic acid is the only acid present)

pH 7.3
CO2 30.1ppm

*KH 20 a difference in 1 pH = 27ppm CO2*


Let's do KH 1

pH 7
CO2 is 3ppm

pH 6
CO2 30ppm

*KH 1 a difference is 1 pH = 27ppm CO2*


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## The Abbott (15 Sep 2010)

Think I need a degree in chemistry to understand all this!  I drop checker arrived today with a bottle of 4dkh with bromo blue from AE. How long will it take once Its filled and in the tank to change colour?????? I take it its best to keep the co2 on 'low' until I have a reading that I can adjust from??

Rich


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## Graeme Edwards (15 Sep 2010)

I have always used a KH test kit, checked that with a PH test and then via a co2 chart. The charts can vary, but you get a good idea of what your co2 is doing. 

I've never heard of what George does. I would wonder how reliable this method was for most people.

Test kits and co2 charts are how I get my readings, that's if I want to know them.

Cheers.


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## George Farmer (16 Sep 2010)

Graeme Edwards said:
			
		

> I would wonder how reliable this method was for most people.


It's the same reliability as using CO2 charts, as it's using the pH/KH relationship.  

The only difference is with this method you don't actually refer to a chart or need a KH test kit, but rely on the pH difference between your CO2 enriched and non-enriched aquarium water i.e. a difference in 1 pH gives 27ppm CO2, no matter your KH.


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## AverageWhiteBloke (16 Sep 2010)

> How long will it take once Its filled and in the tank to change colour?????? I take it its best to keep the co2 on 'low' until I have a reading that I can adjust from??



It usually takes about an hour or to for mine to react, this I know because I take it out the tank when I'm cleaning and I'm going to do a fresh DC (usually every couple of weeks). It is green when I take it out and stick it too my kitchen tiles and by the time I have finished changing water it has gone blue which is comforting as you know it's doing it's job.
Another thing I may mention is that the DC is usually showing what the co2 was from about a couple of hours ago not at that moment.

You could try starting off at say 2bps co2 and aim to have a lime green/yellow DC for when the lights are timed to come on then just adjust up or down from there.

No need for a chemistry degree just yet   the methods George is talking about is just as accurate but as he as mentioned that is only if no other acidic sources are in the tank. Things like bog wood can introduce other acids into the tank so the PH kit will also measure them giving a slightly false result. The DC is generally seen as the most accurate because to only measure free carbonic acid or co2 in the water because the water in the DC is known not to contain any other acids.


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## Whitebeam (16 Sep 2010)

AverageWhiteBloke said:
			
		

> ... the methods George is talking about is just as accurate but as he as mentioned that is only if no other acidic sources are in the tank. Things like bog wood can introduce other acids into the tank so the PH kit will also measure them giving a slightly false result. .


Something in that feels wrong to me (but I'm not an expert in this ) - surely the method George described here:


			
				George Farmer said:
			
		

> 1. Take a sample of tank water in a test tube.
> 2. Shake it vigorously for 60 secs to ensure all CO2 has been gassed off.
> 3. Test the pH. Let's say it's pH 7.6.
> 4. Take another sample of tank water, at an appropriate point in time to ensure plenty of CO2 is present.
> ...


Relies on a pH change caused by the out-gassing of CO2? Unless these other acids out-gas or are somehow destroyed between measurements, the change will only be caused by release of CO2? I agree that the absolute pH will be affected by these other acids, which is why the hardness/pH tables are unreliable, but the change is surely only related to the amount oc CO2?

Peter


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## AverageWhiteBloke (17 Sep 2010)

Yeah you are right, the ph test George mentions has already taken into account any acids in the water so aerating it will just remove the co2 hence the measurement will calculate the amount of carbonic acid that has been removed giving you an idea of what level of co2 was prior to aerating.

I was explaining to the Abbot why just taking a ph and kh reading and cross referencing that with the chart is not that accurate. That'll teach me to read posts thoroughly before posting   next time I'll just keep my daft mouth shut


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## plantbrain (17 Sep 2010)

So how might you verify and confirm the chart or any method?
Eg, how would you calibrate a methods such as any of these?

We can calibrate for a light meter, or a NO3 test kits by usign known standard solutions, but for CO2 dissolved in water at a specific ppm????

Well, we can use DI/RO water, and make a known stock solution of KH, say using sodium carbonate or bakign soda in say a 40 liter volume, add CO2 via a powerhead atomized well mixed tank.

This will have nothing else in the tank other than the CO2 and the carbonate KH.

So this is a referenced system.

Now we can use a calibrated accurate pH meter.

This will yield the correct CO2 based on the pH/Kh/CO2 chart.



Now..........you have a reference to compare your method against.
You can leave the flow rates the same for the RO/DI baking soda reference and add tank water, or if you have a CO2 test.......say a DC or a water sample method with 1 pH unit, you may try that, or a CO2 prove specific meter.
You may change the CO2 reference point by adding/reducing the CO2 gas injection in the referenced system.

This should get most to within 1-2 ppm of CO2.
But......requires folks to actually test and CLAIBRATE THE CO2 AND USE RO/DI WATER MAKE UP, AND A HIGH GRADE pH METER. 

I think it will be tough to beat a high grade pH meter for measuring pH   
What you need to do is to remove the unknowns about the KH/acids etc from the tank system and see what the true CO2 is, they see about scaling that.

DC's are not the best and cannot measure pH very well at all. 

Regards, 
Tom Barr


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## AverageWhiteBloke (18 Sep 2010)

> DC's are not the best and cannot measure pH very well at all.



Tom, thanks for a more accurate way of checking CO2 content, this is something I'm going to give a try just to see what results all three methods come up with as a way of knowing what the DC colour looks like when my co2 level is actually right. Sort of calibrating my DC if you like   More out of curiosity than anything.

I was suggesting to the OP a better way of testing his co2 levels with the equipment he already had until his DC came and then once his DC arrived rather than just taking a sample out of his tank and comparing it to the chart.

Neil


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## plantbrain (20 Sep 2010)

Measuring CO2 is not a simple affair.
I think many of us take it for granted.
and that's about the worst thing we can do as hobbyists.

Adding too much light for the newbies is the other big issue.


Regards, 
Tom Barr


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## AverageWhiteBloke (20 Sep 2010)

> Adding too much light for the newbies is the other big issue.



Indeed, me being a relative newbie I have opted for less light. I was inspired by a friend from works aquarium who was asking me for advice, I called round one night because he asked me to look at one of his fish he was worried about and was amazed at the results he was having with one tube and commercial micros.

That has made me start from the ground up again, I have knocked off one of my tubes out of 3 for the last 3 weeks and the difference to my tank is starting to show already. Less algae and the plants don't look as washed out. Work commitments also mean I have less time to spend on the tank. So my regime is suiting my lifestyle better, I can get away with the weekend water change if I need to.


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## Tom (23 Sep 2010)

George Farmer said:
			
		

> This is way I've done it -
> 
> 1.  Take a sample of tank water in a test tube.
> 2.  Shake it vigorously for 60 secs to ensure all CO2 has been gassed off.
> ...



I tried this test this morning, and found no difference in pH whatsoever, but my drop checker is showing green. Is one of them wrong? My pH is showing 7.5-8

Tom


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## Whitebeam (23 Sep 2010)

Tom said:
			
		

> George Farmer said:
> 
> 
> 
> ...



Previous times I've seen this method described it required you to leave the sample to 'off gas' overnight, rather than shaking for 60s. Try it this way. The other possibility is that your pH test isn't reading properly of course (said that so that Mr Barr wouldn't have to  :silent: ).

Peter


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## AverageWhiteBloke (25 Sep 2010)

Test kits are notoriously bad for doing any serious testing, there are so many variables in getting the wrong result lighting the tester etc. One way of making chemical test a touch more accurate is to use a known solution that is ph7 and see what your test kits says. You might find that the known solution of ph 7.0 actually looks like 6.8 with your test kit   then it gets impossible to back track to what the other value colours will look like   

Getting a electronic ph test kit and some calibration fluid which are relatively cheap on ebay these days would be a more accurate way of going about it (the low PH one's) I spent a lot of time chasing my tail trying to correlate kh/ph measurements and working out the best flow rates for co2 and came to the conclusion that the Drop checker with a 4KH fluid in was ultimately the most convenient. 

To know if you have the right co2 for your particular tank keep increasing the bubble rate gradually while checking the fish for signs of discomfort. Try and get the DC fluid a Yellow/Lime green colour for when the lights come on the tank and to hold it there until lights off and you can be fairly sure that your somewhere near the target. Any signs of lack of co2 related deficiencies or algae try gradually going up or getting better circulation around the plants while watching  the fish, the plants will tell you if your too low and your fish will tell you when your too high.
 A lot more accurate than any test kit I have bought so far.


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