Quote Originally Posted by grimsteph
I have to disagree with Urbanfarmer on the subject of nitrates. There have been numerous studies on nitrate levels and how they impact fish. I actually remembered this from my biology classes as an undergrad, but I did a quick google search and came up with the following from several studies:

- Elevated nitrates above 100 ppm appear to substantially reduce antibody response in fish.
- Elevated nitrates above 200 ppm appear to cause damage to internal organs and particularly kidneys.
- Elevated nitrates above 100 ppm appear to negatively impact growth rate.
- Elevated nitrates at 200 ppm for 7 weeks or more tends to be fatal to fish.
- Elevated nitrates (no ppm given) tend to hamper oxygen absorption in fish.
I am pursuing a Masters of Science in Environmental Science, with a major in Soil and Water, and 2 minors, Aquaculture, and Botany. I have not yet reached curriculum discussing water chemistry as it applies to fish nor fish biology (a course I am very much looking forward to). Yes, my very own custom tailored Aquaponics degree.

With that said, understand I have been left to my own devices until the time comes that I have the above stated education in a state-of-the-art manner. Now, please state any specific research or references otherwise so we can all act as peers reviewing said literature. From the posts in this thread I just reviewed research discussing 200 ppm nitrate on fish. So, please explain... If it is scientific fact that more than 7 weeks at 200 ppm nitrate levels is fatal to all fish in all stages in their life cycle, then how does one researcher state that he observed and studied fish in a commercial operation that consistently had over 200 ppm of nitrate? You would imagine this guy would be out of business with all the fish he has left?

I have yet to see evidence to conclude nitrate is toxic to fish, especially as it applies to Aquaponics.

I don't think it's safe to assume 200 ppm nitrate is toxic or even fatal to fish in any adult stage of their life cycle and sensitivity to nitrate is variably dependent on species and strain for pre-adult stages in their life cycle. FOR EXAMPLE, TILAPIA ARE SUPER FISH.

Anywhooooo, I wanted to thank you from the bottom of my heart for joining the discussion. I think we need more people interested in all our lively debates. With more of us searching out information and presenting it in a forum manner for discussion, I think we can all advance our learning faster and deeper than without each other.

P.S. Was your undergrad in biology or the like? Just curious how much I need to pick your brain.