The temperature was maintained around 24-22 °C, which was the same temperature in my old deep water culture and media bed hybrid system where the fish are still very healthy and eating well. As for the two months prior to their death, they exhibit the following symptoms: lethargy, tended to congregate in a corner, and lack of appetite. When the same exact fish were in the old system they would race towards me when I was regardless whether I was about to feed them or not, but when I approached the same fish in the new system they were indifferent. Food contamination and heavy metal poisoning don't seem likely either because I have been using the same food to feed the fish in my old system and all those fish are still alive and well. Heavy metal poisoning does not seem likely because I had not used any non-food safe products near my systems and the municipal water supplies is known to be clean. Oxygenation was high at all times, ~6mg/l. At this point, I'm almost out of scientific explanations.