How much is my CO2?

[Yo-han]

Like the title says, what is the CO2 concentration in my aquarium? I use a laboratory quality pH-meter and the most precise KH test I can get (Salifert). I know the pH/KH table is quite inaccurate but lets start with that. My KH is 4.8 and pH is around 6.5. According to those charts I've 45 ppm.
Second I've got drop checkers, I used a KH=4 reference and my drop checker is always bright yellow. I made a KH=5 reference solution using sodium carbonate and my drop checker is still yellow, meaning >60ppm CO2.
Third method I used, degassing the water (aerating it for 48 hour). Checking the pH afterwards with the same pH electrode gave me pH=7.38. Less than 1 pH value difference, meaning, not that much CO2...

I do believe I'm low in CO2 mostly because my tank isn't algae free lately and extra circulation pumps didn't make a difference. Any ideas on what my real CO2 value would be? I'm increasing it slowly anyway but my drop checkers shows no difference any more, everything is pearling like crazy an hour after lights on, don't want to harm my livestock just because of some algae...

 

[priv_sim]

I thinking you should test how fast your tank degasses. If its fast (according to this experiment: http://www.barrreport.com/showthread.php/9091-Stable-enough-CO2?p=75110#post75110), you could assume that co2 concentration can stay quite constant through day and you could increase it until fish gets stressed. If degassing is slow, than it gets more complicated to set co2, because there is big chance to kill your livestock and its hard to make your co2 stable.

In short: firstly you should concentrate on stability of co2, after that on amount needed for your aquarium

Well, its my theory...

 

[dutchy]

I also see this contradicting values between pH/KH charts and actual drop checker colour. I experimented with various pH settings and concluded that I couldn't even see a difference on the drop checker with a theoretical drop of 20 ppm.

I also know that if I keep the level to 40 ppm (according to the chart) I get algae like BBA and sometimes hair/thread algae.

So I decided to get rid of the drop checker and not pay attention to the pH/KH chart, but solely look at my plants and fish. To do that I check leaf size of the plants and respiration of fish. Some time ago my cardinals were hiding because I overdid it. Now I know that when they hide, CO2 is too high. I just keep it a little bit lower than that point, which is around 0,1 pH. So in my case there's a thin line between max. plant development and min. fish stress.

To give the pH/KH chart readers an idea, that ended up in pH 6,4 with a KH of 6, which is a theoretical CO2 value of 76 ppm. High? yes. Too high? Probably not. Even my Amano shrimp are active and doing well. But I also have at least 8 ppm of O2 in the tank.

What I'm trying to say is that it's possible to do it without worrying about the actual level. There are lot of live indicators that will exactly tell you what to do.

 

[Tom Barr]

FYI, the method I use most, but adjust things very slow and progressively, is the same Dutchy uses.
My 180 sits at 70 ppm of CO2, the 120, maybe 50 ppm, my old 60 Cube had about 50ppm etc.



Only then.........do I attempt to measure things.

You need a good plant growth, healthy fish reference.
This will be different for every aquarium unfortunately near as I can tell.............
O2 plays a factor etc. Plant type and biomass, nutrients, on and on........

If you know you get great growth at say a pH of 6.2 with the KH of 3 degress, say 54 ppm...alkalinity...........
then this is a reference, but it's relative to that specific tank.

You can try Dry ice in a sealed flask etc and use the weight of frozen CO2 which will melt ........in a known volume of water/gas space.
Then measure the solution(aquarium water) with a pH probe and compare/repeat this vs a KH standard solution as well.

A rubber stopper with a pH probe sized hole and a flask, say 1 liter.............a scale(accurate to say 0.001 gram or 1 milligram) would work fine.
Dry ice can be bought at many grocery stores and party supply places, etc.