The maximum concentrations depend on how long fish are exposed. Generally, tilapia should be in water with CO2 levels of 3+ mg/L for optimal growth, but can tolerate short exposure to 0.3 mg/L. Ammonia concentrations as low as 0.08 mg/L can start to reduce food consumption, but in concetrations of 2+ mg/L significant die can occur. Ammonia should be kept under 0.05 mg/L for optimal growth. With nitrite, chloride concentrations affect the toxicity of ntirites - low chloride concentrations mean lower nitrite toxicity. See http://fisheries.tamu.edu/aquaculture/tilapia-production/ for more information on tilapia production.

Thank you very much for the response.
1.  On CO2, if 3+ is a minimum, what is the max.
2.  I assume the ammonia numbers you are talking about are for non-ionized NH3? Converting to total ammonia which we are currently testing would include a factor of 40x at pH 7.5 according to one table I found. We are running from 0.5 to 3.5 total ammonia which would above your recommended numbers (with 40x conversion) but well below the 2ppm max. Is this correct.

Again, thanks so much for your response - you are very kind to help us out.

#1> I goofed on that. That's the minimum DO number. CO2 should be under 40 mg/L

#2> The initial source I looked at wasn't clear on what form it was talking about. I doubled checked another source (http://fisheries.tamu.edu/files/2013/09/SRAC-Publication-No.-282-Tank-Culture-of-Tilapia.pdf). They are much clearer: for non-ionized NH3, you really want it below 1 mg/L.

I apologize for the confusion.