Interesting, but isn't that 100 mg/l nitrate a bit extreme? Is there a danger that water quality gets dangerous to fishes? I guess nitrite was ok, but did you measure pH, KH, ammonium just to be sure? Do you know measured water values in Amazon rivers at dry season? I'm not criticizing, just interested.the water after 2.5 months dry season was very charged with Nitrates (around 100 mg/l), the color of water turned out around dark yellow, but with a good flow and a venturi, the oxygen saturation was very high all along...