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Re: CO2 measurements

On Thu, 25 Nov 1999, Michael Laflamme wrote:
> I currently have a 65 gallon tank with a wet/dry filter and pressurized C02 
> being fed at 15mg/ltr, according to the gauge.  I understand the 
> relationship of pH, dkH, and C02.  My pH is 6.8 and my dkH is between 3 and 
> 4.  I also have peat in the substrate, which Tom Barr informs me will negate 
> the pH, dkH, and C02 equation.

Well, *might* negate the pH-KH-CO2 relationship.

> So, my question is; if I test with a C02 
> test kit what readings will indicate adequate C02 in the water column?  
> Also, what exactly are these readings telling me?..i.e what readings show 
> too low C02, or too high C02?

If the peat is causing a problem then it will cause your CO2 determined
from the pH-KH-CO2 relationship to be slightly high.  I suspect (but can't
prove) that you don't need to worry about the peat causing you any
problems unless your water is rather deeply colored by the peat.

Peat only causes a problem if it contributes measurably to the KH.  One
way to check is to measure the KH of the water you use to fill the tank
and the KH in the tank itself.  If the values are the same then the peat
isn't intefering with your test.  In fact evaporation can make the KH in
the tank higher than KH in your water source and you still don't need to
worry about it messing with the test.

> My plants are doing extremely well, but I 
> only see pearling on the upper most leaves of my plants.  It makes me wonder 
> if more C02 might be helpful.  However, when I have gone higher than 
> 15mg/ltr, the pH gets too low.

If your plants are bubbling at the top, but not elsewhere then it's more
likely that your lights may be a little dim for your plants or that you're
not getting enough light penetration.  As long as the plants are growing
well and look healthy you don't need to worry about adding more CO2.

There are so many variables that go into determining whether plants will
bubble that bubbling is a poor measure of conditions in the tank.  You can
have perfectly healthy plants without much active bubbling and you can
have active bubbling in tanks where the plants are growing poorly.  It
just isn't a very good indicator of your plants' conditon.

Roger Miller