I bought my male Dwarf Gourami 6 months ago and the pet store reassured me he was passive. Even saying he was extremely passive. He was fine with the other fish at first but he would wake me during the night thrashing the tank themometor. I couldn't figure out how he was doing it I just knew he was. About 2 months after getting him I got a bottom-sucker and within 24 hours one of my fish died and the rest followed each within 24 hours till all were gone (including bottom-sucker) leaving only the Gourami. I thought it might have been due to the filter so I waited a while before I bought anymore fish. About 2 months ago I ourchased some more (all passive-according to the pet store) and the same exact thing happened. It starts 24 hours after I've put them all in together and then they all die, one by one, within 24 hours of each other and they don't float to the top so I know they must have been killed close to the bottom or the filter system wouldn't have picked them up. The bottom feeders sink to the bottom leaving only the Gourami left. I have a 15 gallon tank and am convinced and confused that my Gourami would feel the need to kill them. He doesn't thrash the themometor anymore but I know that is how he must be killing them. It's too similar to be just coincidenous.Can this truly be possible? And if so then why wasn't I warned? r do I just have a psycho fish-LOL?