I have a 20 gallon aquarium and have had nothing but problems with it since I got. At this point, I'm pretty sure it's possessed or something. (The last guy that had it had problems with it too). I've had this tank up for about 2 months. It was doing really well up until 3 weeks ago, when my water turned really cloudy. Not sure why. I did a partial water change. No help. I bought a new filter, Fluvel C3. (I've had the filter in for less than a week and is telling me I need to change it out.) No help. I did a full water change. For about 12 hours it was fine. After 24 hours, it's back to the same state. I use Tetra Aquasafe and Tetra safe start in it. But I don't put anything else in it. All my levels have been fine. Before my change ammonia was at .25 and my nitrate and nitrite was at 0. pH was at 7, perfect for tropical fish. I keep my water at a toasty 80 degrees F. I have a Betta, 2 glowlights, and a snail in this aquarium. What am I doing wrong!? Or is my aquarium haunted? I keep my 5 gallon in perfect condition. I am really close to selling this one and getting another 5 gallon for my Betta.