I recently purchased a fish tank. It is a 5 gallon with a Tetra Whisper filter. I added water conditioner and some de-stress stuff after letting it cycle for 48 hours. I then went to get some fish. This is, of course, before I learned about cycling and all those good things. No one at the pet store mentioned it and neither did the instructions that came with the tank. Anyway, I ended up with a molly, 2 platties, and 3 guppies (probably too much for a 5 gallon?) My fish have been in there for about 5 days now. All of the guppies died, but the platties and molly seem to be doing great. I have been checking the water almost daily and my ammonia, nitrite, and nitrate is very very low and I have a neutral PH. I found it weird that only guppies died. Before they died, they hung out at the top gasping for air with their gills. The water seems to be in good condition, so I was wondering maybe my tank isnt getting enough oxygen for the guppies and maybe the molly and platties can get by with less oxygen? Would purchasing an aerator be a good idea? Thanks for any help. 
