About 2 weeks ago I lost my male dwarf gourami. The night before he seemed fine, he wasn't sick, was eating and swimming around like normal. When I found him in the morning he was just laying at the bottom of the tank. I didn't see any signs of illness, no wounds or anything. I had him for not quite a year. So I thought well I'll do a water change and get another fish for the tank. So I performed about a 25% water change and waited for a few days and got one platy and 2 female guppys (I decided to get my male guppy a pair of females). They all seemed to get along. Of course the male was happy and was following them around at first. I had them together for almost a week and then my female dwarf gourami died. There was nothing wrong with her that I could see. She was acting like she normally did, she ate that morning and then when I came home from work later that afternoon I found her at the bottom of the tank. Then this morning I fed the fish and I couldn't find my male guppy, I looked around the tank to find that my one amano algae shrimp was eathing his dead body. I did another 25% water change this afternoon. I did test the water when the male dwarf gourami died and the water looked ok. The ammonia was at 0, the nitrites was at 0 and the nitrates were around 25 to 30. So the water looked to be normal. what would cause 3 fish to die in about a two week span? I've never had problems with this tank before. This is my 20 gallon tank. Right now I have 2 amano shrimp, 2 female guppy, 1 female platy and 2 snails.