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How to reduce CO2 in DIY CO2 system


I've just created my first DIY CO2 system following the many articles
available on the web. It's been working great: in just 2 days the plants
have grown several inches (!), they are all bubbling away with oxygen, etc.

Right now I just have a bottle with water, sugar, and yeast, connected
with an air tube to a stone at the bottom of my 29g tank. I'm using
the suggested proportions of 6 cups of water, 3/4 cup sugar, and 1 tsp
of yeast. 

Even though I haven't created any sort of CO2 reactor yet, I believe that
I'm getting too much CO2 in the water. My bottle seems to put an almost
continuous stream of bubbles (through the air stone), and I've heard that
I shouldn't go any lower than 1 every second or two. If I didn't have the
stone I imagine it would be several bubbles per second. I also notice that
my pH by the end of the day has gone from 7.0-7.1 (my normal tank pH) to 
6.6. And that's during the day while the plants are bubbling away like crazy.
I just don't dare to leave it on during the night. I fear I would find 
a pH of 3 in the morning! I didn't think I had particularly soft water
either (I even thought it was on the hard side--I'm in Amherst, central
Mass), but I don't have a measuring kit for that.

I would like to hear other people's solutions to this problem. Ideally I
would like to leave it on, making one bubble every 5-10 seconds or so
(that way it would last longer too). I've cut down the amount of yeast
to 1/2 teaspoon while keeping the proportions of the other ingredients,
but it hasn't slowed it down appreciably. Should I lower it even more?
Should I cut down on the sugar? Room temperature is around 65F.

I thought of using some simple air regulator (like the ones used with air
pumps), but I didn't think that would work. Closing the tube a bit would
momentarely reduce the amount of CO2 delivered to the tank, but since more
is being produced, the pressure inside would increase and more would be
delivered again to the tank.

For the moment I can only think of unscrewing the tube at night, and 
reconnecting it in the morning. That way I avoid poisoning the fish,
but it produces quite a pH change. 

I don't feel up to doing Gary's electronic regulator quite yet. I was
hoping for an easier solution for now. But who knows, I might end up 
doing something like that in a few months.

Any help would be appreciated. 

--Noel, now completely converted to using CO2 :)
llopis at zonker_ecs.umass.edu