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CO2 levels from Yeast Method CO2

Hello everyone,

I've recently set up a number of 20 Gal. tanks for study purposes and I am
using individual 2 L. Yeast Reactors for CO2 supplementation. I've used this
same method of CO2 fertilization on my 120 Gal. tank for over a year and a
half with no problems. (1 L water + 2 cups of sugar + 1 tsp Baking Soda + 1
tsp Dry Yeast)

In the past (on my 120 Gal tank), I usually ended up with CO2 concentrations
of between 15-20 ppm CO2 by using a homemade reactor where the CO2 gas gets
mixed with the water prior to entering the main aquarium. In this instance,
I am feeding the CO2 from the Yeast Reactor into the intake stem of a small
external power filter (Eheim Aqua Boss, very similar to a Hagen Aqua Clear
200). The gas enters the intake stream and gets forced into the water as it
passes thru the impeller chamber of the filter.

All water chemistry tests are made using either LaMotte (pH, O2) or Hach
(Alkalinity, Hardness - Total, Calcium and Magnesium) test kits and the
tests were repeated twice in most cases to ensure accuracy.

Prior to adding the CO2 to the systems, I measured the CO2 concentrations of
the indivdual tanks for a number of days to determine a base point for CO2
concentration in the water at equilibrium with the atmosphere and discovered
that the tanks contained 6-7 ppm CO2 naturally. Since adding the Yeast
Reactors, the CO2 levels in each tank has shot up to anywhere between 45-56
ppm CO2. The indivdual tanks contain (variously) between 100-150 ppm
Alkalinity (in most cases, I added Baking Soda to several tanks to increase
the Alkalinity in order to prevent a pH drop. The ph values of all the tanks
is stabilizing at 6.4-6.6 after almost a week of CO2 injection.

Dissolved O2 levels in all tanks is similar, and stable, at 8.7-9 ppm O2.

At this point in time, only one tank contains any fish - an adult female
Variatus Platy and 2 juvenile Praecox Rainbowfish. The fish show absolutely
NO signs of distress due to the high levels of CO2 in the water. Their
breating is normal, their movements match fish in other tanks without this
level of CO2.

Everything that I have read indicates that levels of CO2 of this nature can
be dangerous. Should I take some action (aeration of the water) to drive off
some of the CO2 in these tanks, or just leave well enough alone? I assume,
as it has been my experience with Yeast Method CO2, that the output of CO2
will decline over time, but should I wait for this to occur naturally?

The plants in the tanks, although just recently planted, are showing every
sign of settling in properly and are beginning to grow (no sign of excessive
algae growth yet) and I have seen O2 bubbles trapped in several thickets of
Ricca in one of the tanks several hours after the lights are turned on.

How have other people who are using the "DIY" pop bottle method of CO2
production found their CO2 levels? Have I perhaps chanced upon a secret
strain of "super yeast"?


James Purchase
Toronto, Ontario
jpurch at interlog_com