I had successfully bred Oscars for a few years before moving into my first apartment and no one wants a 2 ton aquarium above their head so I had to abandon my hobby. My daughter just turned 2 and she loves fish so I got out one of my 30 gallon tanks and a heater and the best filter I had for that tank and set it up. About a week later I introduced 8 mollies from my local pet store. For the first 2 weeks everything was fine they all were ravenous eaters and seemed to work well as community fish, no nipping or chasing. The past week has been a complete downhill spiral. Every night I notice one or two of the fish hiding in the cave or in the plants, not coming out to eat and acting very spooked if another fish swims by and in the morning they are dead. They are showing no sign of sickness and other then hiding before their demise they aren't acting strange. Any help would be appreciated.