Re: Info on C02 Injection Needed

> From: Marty Durkin <durkin at stsci_edu>
> I have setup a DIY-Yeast C02 Injection system in a
> 1 gallon bucket to test things out.  The water initially
> had a ph of 7.5, a KH of 3, and a GH of 6.  The C02 injection
> has actively been injecting CO2 through an airstone since
> last Saturday.  As of Wednesday evening, the ph had dropped
> to 4 (I used 2 separate test kits to test it).
> My question is, since I will be using this on a 55 gallon tank, 
> will the ph drop as drastically since I am dealing with a much 
> larger volume of water.

No. The pH drop is strongly correlated to the amount of CO2
dissolved per volume of water. An entirely safe amount of water,
sugar, and yeast for a 50 gallon tank is:
1.75 liters of water, 2 cups of sugar, 1 tsp of yeast, and
1 tsp baking soda (assuming room temp ~75F)

> I'm concerned that I will kill my fish if I add the C02 injection
> to the tank.  

Stop worrying. Lots of people use it. I suppose you would kill
fish if you had 50 liters of water in a yeast jug with 100 cups
of sugar and 50 tsps of yeast. :-) It is very difficult to 
determine by small scale experiments how much CO2 you will be able 
to dissolve because of factors like the surface area of the tank
water, the amount of surface motion of the tank water, whether
there are floating plants, air injection by airstone (don't),
surface turbulence (minimize), or wet/dry style filters (don't).
Your KH is nearly optimal for CO2 and will provide a degree of
pH buffering. Aim for 10-15ppm of CO2. The LaMotte CO2 test kit
is quite accurate. Some others (like Tetra) are not.

If your room temperature is very warm, it might be wise to start
with less water and sugar to reduce the initial amount of CO2.
After a week or two add a second bottle in parallel with the
first when the CO2 production starts to drop off. This helps
to stabilize the yeast CO2 production.

In general, you do want to maintain under surface water circulation
for the benefit of the plants and maintain particulate filtration.
You may want additional biological filtration if you have a heavy
fish load but most aquatic plant enthusiasts don't over stock
since it can contribute to algae problems. With the proper ratio
of fish, plants, light, micro-nutrients and CO2 you do not need
any biological filtration and it may actually contribute to algae
problems by producing unwanted nitrates in solution.

Vancouver Steve  (more skiing weather on the way :-)