My 44 gal bowfront tank that I've had for well over a year now, suddenly turned very cloudy and green. I haven't added new fish or plants. I did a big water change Friday and cleane the tank and changed the filters. Sunday it was still cloudy and greenish, so I did another water change. Here it is Tuesday and it looks the same if not worse. I did a water test and all levels are normal according to the apI master test kit. When I got home from work tonight I see all of my guppies are grouped together on top of the water. I don't know what to do.