I came home and he was lying in the bottom of the tank; I freaked on the wife and kids, thinking someone put something in the tank. But that was a error on my part; all the other fish were fine. I checked the parameters; everything was at 0 ppm except the nitrates, which was 10 ppm. I am told less than 40 ppm for nitrates is accceptable. Ph was 7.5, temp was 80. The wife said she heard a splash and bang on the glass but thought nothing of because the pacus are always chasing each other. Now we think the o was spooked and launched himself against the glass, fatally...
