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re: DIY CO2 Injection

From: "Jan Fidrmuc" <J.Fidrmuc at kub_nl>
>
>I have already leart that DIY CO2 injection can be made from 2L soda 
>bottles and that the mix should be 2 cups of sugar, 1 tsp of baking 
>soda and 1 tsp of yeast. I understand the bottle should be filled 
>almost to the top with watter then. 

The measurements you indicated are the ones I use, so I'll add an extra
comment.  I do not attempt to control the cottony bacterial buildup that can
occur in yeast CO2 systems.  I understand that filling the bottle to nearly the
top can encourage this growth.

>Besides the composition of the mix, 
>does the temperature matter much? I have some of my tanks in 
>a rather cold room - the tanks have heater though. 

From what I remember of chemistry, 10 degrees Celsius is roughly equal to
doubling any given reaction rate, so yes, temperature will have an effect on
the rate of production.

>And, is it possible 
>to kill the fish by injecting too much CO2 - either by making the 
>carbon dioxide replace oxygen in watter of by making the Ph drop too 
>much? If so, how can I controll how much CO2 is injected with this 
>setup? 

It is possible to kill your fish by injecting too much CO2.  CO2 does not
replace dissolved O2 in water, it can just reach lethal doses in extreme
circumstances.  If I remember correctly, 30 ppm is approaching lethal doses in
at least some fish.  15 ppm is the usual desired amount for a brightly lit
plant tank, and atmospheric balance is around 2 ppm if I remember correctly.
You can measure your CO2 levels by measuring your KH and your pH and consulting
the table at the bottom of the CO2 FAQ, located at:

http://www.cco.caltech.edu/~aquaria/Krib/Plants/CO2/co2-booth-faq.html

>Finally, I understand the CO2 will make the Ph drop. Should I 
>counter this by adding some baking soda to the tank watter?

My goal is KH=5 and pH=7.0.  My tap water makes the KH portion easy, but I
don't always inject enough CO2 most of the time to get the pH down to 7.0.
This combination works out to 15 ppm CO2 in the water.  With my yeast system, I
adjust the efficiency of my CO2-water reactor mechanism to try and balance out
the pH at 7.0.

I hope this helps,

David W. Webb
Enterprise Computing Provisioning
Texas Instruments Inc. Dallas, TX USA
(214) 575-3443 (voice)  MSGID:       DAWB
(214) 575-4853 (fax)    Internet:    dwebb at ti_com
(214) 581-2380 (pager)  Text Pager:  pgr at ti_com Subj:PAGE:David Webb