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Re: CO2

> Date: Thu, 3 Aug 2000 16:32:11 EDT
> From: FocaIPoint at aol_com
> I'm about to jump off into the unknown once again and would like to receive 
> the collective list wisdom on the following.
> Saturday when my Bioplast regulator etc arrive, I'll be hooking up my CO2 
> system for the first time. I'm aiming for 10-15 ppm of CO2 and will probably 
> start the perking at one or two bubbles a second. Reasonable? Or am I totally 
> off in left field here?

15 ppm is a great goal. I hope you plan to measure CO2 directly or indirectly 
and don't depend on "bubbles per second" as an indicator of proper CO2 levels. 
> Not trusting them darn tables, I 
> went out and bought a Sera CO2 test kit.

Is this the one we never hear good things about?  Trust the tables, but be wary 
of your measurements!

> PO4 - 0 to 0.5 ppm

Phosphates in your water will be seen by your "KH" test kit as additional KH. 
It's not really KH, but additional alkalinity. Remember, KH test kits are really 
measuring total alkalinity with the assumption that carbonates are the only 
contributor. If you have phosphates in the tank, this assumption is false. Be 
careful here. 

The CO2/KH/pH tables assume that the only alkalinity is from KH. If you have 
phosphates, the tables will NOT give you correct results. 

It wouldn't hurt to measure pH, CO2 and KH and see if what you measure 
correlates to the tables (account for the error ranges of your test kits). It 
would be good to check your test kits against reference solutions. Never trust a 
hobbyist grade test kit until you have verified it! Most of them suck. 
> With the following tank parameters, what can I expect regarding pH and 
> hardness changes. (I'll be turning the system off at lights out)
> pH - 7.0
> dkH - 4.0
> Am I correct in expecting a .5 drop in pH to circa 6.5, and how will this 
> affect gH and kH? 

No, with a KH of 4 and 15 ppm of CO2, you will get ph = 6.9.

CO2 does not affect KH. KH is an independent variable. The amount of CO2 
injected against a certain KH will then determine the pH. You can juggle KH and 
CO2 to pick the pH point you want. Usually, folks will want 15 ppm of CO2 for 
good plant growth and will then select a KH that will give them the pH they 
want. KH generally has no or little effect on fish or plants, so it is the 
reasonable variable to change.  

CO2 does not affect GH either. GH is independent of the whole pH/KH/CO2 thing. 

> I learned a bitter lesson early on, and I am loth to add 
> ANY chemical to the  water column unless absolutely necessary, and I mean 
> absolutely.

You are correct to be wary of adding chemicals to the tank. But you are 
incorrect in being so adament about it.  Adding sodium bicarbonate is a 
perfectly reasonable thing to do to increase KH. But, of course, you should be 
cautious to measure carefully and test afterwords to make sure you add th 
correct amount.

Likewise, calcium carbonate is a fine way to increase GH *and* KH and is, in 
fact, the way nature does it. Measuring carefully and testing afterwords is also 

And you might want to research your idea of turning off CO2 at night. It is 
worse for tank stability to stop and satrt CO2 than it is to leave it on all the 
time. Assuming, of course, you have good control of the flow of CO2 entering 
your tank. 
Good luck with CO2. You sound like a careful person so it should work out well 
for you. 

George Booth in Ft. Collins, Colorado (booth at frii_com)