Setting up a high school with an RAS. I'm excited!

Also, after the initial use of the available nitrates, will there be sufficient additional production from the fish population to support the plants? I suspect that unless you are running a hugely intense fish production and minimal aquaponics, there will not - however I have been wrong sufficiently in the past that if we were keeping score I would win hands down against everyone in this forum...

Mike,

It's a balancing game from what I understand, but the biological filter produces a continuous supply of nitrates due to the ammonia produced by the fish directly or indirectly (gills, feces, urine, uneaten feed etc.). The fish feed itself also produces phosphates.

You're spot on except for your contention that nitrate is toxic to fish over 40 ppm. It has to be over several hundred for that -- at least in the species that I raise: centrarchids and yellow perch.

I think you are thinking of acute toxicity. Nitrate at 200 ppm will cause blindness within a week or two, yes. The long term toxicity level is much lower, though. This article http://www.oscarfish...e-toxicity.html did a pretty good job at convincing me that nitrate at 40 ppm is not safe long term for fish. I would copy and paste it here but it's pretty long. I will copy and paste their reference citations, though, because I understand that not all articles on the internet are accessible for all time.

References
1. Camargo, Julio A., 2004, Nitrate Toxicity to aquatic animals: a Review with new data for freshwater invertebrates, Chemosphere 58 (2005) 1255-1267
2. Colt, J., Tchobanoglous, G., 1976. Evaluation of the short-term toxicity of nitrogenous compounds to channel catfish, Ictalurus punctatus. Aquaculture 8, 209–221
3. Edwards. Thea M., 2006, Water Quality Influences Reproduction In Female Mosquitofish (Gambusia holbrookie) from Eight Florida Springs, Environment Health Perspectives, Vol 114, Supplement 1
4. Hrubec, Terry C., Nitrate Toxicity: A Problem of Recirculating System, Aquatic Medicine Laboratiry, Virginia-Maryland Regional College Of Veterinary Medicine.
5. Kincheloe, J.W., Wedemeyer, G.A., Koch, D.L., 1979. Toler- ance of developing salmonid eggs and fry to nitrate exposure. Bull. Environ. Contam. Toxicol. 23, 575–578
6. Scott, G., Crunkilton, R.L., 2000. Acute and chronic toxicity of nitrate to fathead minnows (Pimephales promelas), Cerio- daphnia dubia and Daphnia magna. Environ. Toxicol. Chem. 19, 2918–2922
7. Shimura, Ryuji, 2004, Nitrate Toxicity on Visceral Organs of Medaka Fish, Oryzias latipes : Aiming to Raise Fish From Egg To Egg in Space, Biological Sciences in Space, Vol. 18 No1 (2004):7-12
8. DELLAMANO-OLIVEIRA, Maria José, SENNA, Pedro Américo Cabral and TANIGUCHI, Glória Massae. Limnological characteristics and seasonal changes in density and diversity of the phytoplanktonic community at the Caçó pond, Maranhão State, Brazil. Braz. arch. biol. technol. [online]. 2003, vol. 46, no. 4 [cited 2006-11-03], pp. 641-651.
9. Mayorga, Emilio, 2002, Processing of Bioactive Elements in the Amazon River System, The Ecohydrology of South American Rivers and Wetlands. IAHS Special Publication no. 6, 2002
10. Lewis, William M., 2006, Concentration and transport of dissolved and suspended substances in the Orinoco River, Biodegradation Volume 7, Number 3 / May, 1989, 0923-9820 (Print) 1572-9729 (Online)

Edited by EricaWieser, 24 October 2011 - 08:20 AM.

I am not sure where I read it, but there was a study done showing that centrarchids are hugely nitrate tolerant and are also one of the most nitrite tolerant fish, almost immune to brown blood disease.

I am not sure where I read it, but there was a study done showing that centrarchids are hugely nitrate tolerant and are also one of the most nitrite tolerant fish, almost immune to brown blood disease.

True! So are percids to some extent. At least according to a fish pathology book I have. I think Erica is right but at the same time if depends on the species. I've had nitrates well over a hundred in my system before and my perch and bluegill were happy as a clam (whatever that is).

I had a situation this summer in a very small holding pond where I had too many bluegill and yellow perch. I knew I did, and needed to remove some, but never got around to it. At some point in the summer when water temps approached 90 F. my ammonia climbed to 4 ppm and the nitrites were 2 ppm. Keep in mind my PH is quite high at 8.5 so unionized ammonia wasn't at a good level either. Nitrates were very low under 5 ppm but that's normal in a pond with lots of algae ad some vegetation taking up nitrates. Like an idiot I was also feeding heavy until I realized something was wrong as they backed off the feed suddenly. I wanted desperately to flush the pond with my well but it was down.

Anyway the interesting thing was the only fish that were showing serious stress were the largest yellow perch which I was able to remove with a dip net to a pond with better water quality. (They were anoxic). My well driller showed up and fixed the well and after flushing the pond all was well again. But the interesting thing is the bluegills didn't show any serious signs of distress other than backing off on feeding.

As far as I know all the fish came out of this in good shape. They've all feed well since then and have excellent condition factors.

I have since read that fish can acclimate to elevated ammonia and nitrite levels if given enough time. Perhaps that is what saved me this summer to some extent.

Just for the record the flushing of this pond did not go into some public water way or anything. I feeds into another pond that is 10 times larger.

Edited by az9, 25 October 2011 - 08:22 PM.