Ok here's the scoop. I have a 60 gallon tank, with a Penguin 350 bio-filter, and also an undergravel filter with 2- 1200 Maxi Jet powerheads. Everything was working perfect and when I left my house yesterday morning about 10am the water was perfectly clear. When I got home from work, about 6pm, it was cloudy (like fog cloudy). Checked the tank and the ammonia was a 4.0 it's a new tank so I expected that. So I did a water (about 30-40 percent) change on it. I put Ammo Lock in the entire tank and this morning when I get up and turn on the light it is so cloudy you can barely see anything. I just don't understand why all of the sudden it got cloudy. Does anyone know why do tanks do that? I have a 29 gallon and have NEVER had that problem. So please tell me what is going on and what I am doing wrong!!!! Any help appreciated, and thanks in advance!