Tank details would be very helpful!
To me though, it sounds like a bacterial bloom.
How long have you had the tank set up? If the tank has recently been set up, then it is most likely a bacterial bloom. There are a couple different types of bacteria that grow in our tank(s), the ones we want are called Autotrophic bacteria. These bacteria live in the filter and process ammonia produced by your fish and other rotting debris in the tank. Another type of bacteria that sometimes grow for a short period of time are called Heterotrophic bacteria. These bacteria are larger and grow at extremely fast rates, way faster then Autotrophic bacteria. What happens is, when a new tank is set up and a water conditioner is added to the tank, the water conditioner immediately makes the water safe for life by breaking down all the harmful elements and stuff. Then the Heterotrophic bacteria quickly go to work on the organics in the water. So these bacteria, the ones we don't want, begin to eat the organics in the water. These bacteria are so large in fact that they cannot attach themselves to surfaces, so they are free swimming. So what you are seeing is actually millions of bacteria, which make the water look cloudy.
This is VERY common in new tanks, and not harmful. After the organics in the water begin to diminish, and the Autotrophic bacteria begin to take hold, the Heterotrophic bacteria will die off, leaving the water clear.
Let us know you tank details and then we will be able to tell you if what you are experiencing is in fact a bacteria bloom or something else?
-FHM
