Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Heterotrophic bacteria grow in cycled tanks, too, have nothing to do with the nitrogen cycle. They feed on organic matter including skin oils when you set up a new tank, which is why people think they are related to uncycled tanks. If you recently disturbed the substrate that could have released some material that these bacteria feed on, so the population has risen to take advantage of the food. It will go away.
Green water algae starts by looking sort of white-grey. It turns green pretty fast, though.
Fish disturbing the substrate can cloud the tank. Digging fish, or larger highly active fish can do this. This sort of clouding usually goes away very quickly unless the fish keep on digging.
Rising ammonia can make the water cloudy. Often there are bubbles at the surface that linger a bit longer than ordinary bubbles.
pH altering materials can cloud the water. If the water company changed something in the way they handle the water that might do it. If you added a rock or a shell to the tank, or pH altering products, that could do it.
I would test with all the kits you have, but especially ammonia, pH, GH and KH. Obviously if the ammonia is up you will need to do plenty of water changes and perhaps add some nitrifying bacteria to deal with it. Ammonia may be from a dead fish or an accumulation of food, perhaps trapped where the fish cannot reach it, so do a pretty thorough cleaning.