Re: CO2 Levels

These are the exeriences I have had with CO2 levels using tetras, barbs,
and clown loaches as guinea pigs (I have never purposely experimented on
them - These just happen to be instances of equipment malfunction, human
stupidity, etc...)

15 mg/l - ideal for plants.  Fish are fine.
25 mg/l - same
30 mg/l - same
38 mg/l - fish begin to react with increase gill activity.
40 mg/l - fish begin to react with obvious distress.
45 mg/l - immediate water change required.

Measurents were taken using Hach CO2 test kit, (standard checked), so I
know they were accurate measurments.

In all cases of distress, the fish recovered nicely, with no long term symptoms.

BTW, the environment the fish live in is pristine, 25% water change weekly,
they are fed live foods, etc.. Therefore, their recovery may be a function
of the environment as well as timely human intervention.

Augustine Rodriguez
Elk Mound, WI, USA