Re: Problems with DIY CO2

Tom Misiak asks:
> 	I have two planted 55 gal (All Glass 48"x12"x12") tanks.  
> water is very soft, has a Kh of less than 2, and Ph of about 6.8-7.0.  The
> tanks are both lit with 80W of flourescent light (1 triton, 1 vita-light).
> I have been using DIY CO2, but it only lasts 5-7 days before
> it needs to be changed.  Also, due to my soft water and its low Kh, I've
> had to use baking soda to increase the Kh to minimize Ph fluctuation. 
> Okay, here are my questions:
> 	o my light is only moderate, is the CO2 at these levels even
> helping things enough to justify its use and the instability of Ph it's
> causing at this time?

In my experience, yes. Many types of plants can and do resort to biogenic
decalcification to obtain CO2 and this was the case in my tank with nearly
identical conditions to yours. (I recently upgraded to 250w MH but that's
another story) I was experiencing very high (alkaline) pH levels although
my tap water is more acidic than yours and also very soft. There was a
noticeable increase in plant growth and the ability of the plants to
effectively compete with the algae. I have also observed lower algae
growth rates when CO2 maintains pH below 7 although this might be attributed
to the pH and/or increased allelochemicals from the plants.

With the increased lighting in this tank and attempting to maintain pH
at my target of 6.7 with CO2, there seems to be an increase in algae
growth: 1) thread algae (tough green strands on the substrate and around
the bases of plants 2) brush algae on certain plants: Echinodorus sp.
sold as E. amazonicus and the stems and older leaves of C. wendtii.
An unclassified specimen of what is either Ammania or more likely a
variety of Ludwigia was also badly attacked by a dark furry algae,
probably brush algae, on the older leaves. The new leaves are very
reddish and have a different form. More on this plant later.

> 	o I can't afford a "real" CO2 setup, if I continue using DIY what
> can I do to eliminate Ph fluctuations and stress to my fish and plants?

One method which you are using is pH buffering using sodium bicarbonate.
Can anyone help out with some good advice on this subject? The second
approach is to use two CO2 generator bottles ganged together and alternate
sugar-yeast changes each week or 10 days. I also understand that brewer's
yeast supplement (is it vitamin B?) increased yeast longevity. Another
approach (slightly more wasteful of sugar) is to empty half the yeast
bottle each week and add fresh sugar and water. The idea is to have
uniform yeast activity. I hope this will be helpful.

I have a question: when is it appropriate to use calcium carbonate
instead of or in addition to sodium bicarbonate? How much should be
used and is it used up? Your helpful advice is appreciated. ;-)