You might experience a cloudy tank, experienced fish keeper or not. No matter how many water changes you do, nothing works, and your beautiful aquarium looks like you poured milk into the water. Microscopically you have autotrophic and heterotrophic bacteria. Autotrophic bacteria are bacteria that can synthesize their food. These bacteria are collectively known as your "good” nitrifying bacteria. This bacterium is structurally smaller than its counterparts and attaches to everything with surface area in your aquarium. Slow to reproduce 15-24 hours, this bacterium oversees converting ammonia to nitrite and then nitrate.

On the other hand, you have heterotrophic bacteria that are the first to establish in your fish tank. These bacteria cannot produce the food and energy it needs to sustain themselves. These "bad" bacteria act like the decomposers of your aquarium; this bacteria feeds on organic material like uneaten fish food or waste in your fish tank. Also, heterotrophic bacteria are responsible for creating the biofilm you see as a film on the water surface or a white "moldy" looking film on driftwood or other organic material in your tank. Biofilm is a build-up of proteins from organic matter. Sometimes you are unaware; you lose a fish or have an overload of dead organic matter in your aquarium or add too much fish food and see a milky bloom in your aquarium. There are heterotrophic bacteria in your water column and when active. You will see these bacteria at work in your water column, which is the milky coloration you see. This bacterium is quick to reproduce every 15-20 minutes. However, if the food source runs out, the bloom will dissipate.

When starting a new aquarium, helps to use media, plants, or substrate from an old aquarium. Ideally, you should use material from another aquarium because of all the beneficial autotrophic bacteria attached. Once in the new aquarium, this bacterium will begin to colonize the new tank. If you add too much organic matter or fish that produce a lot of waste, the heterotrophic bacteria will reproduce faster, and a cloudy tank will likely rise.

If you have fish in your aquarium, you must change the water because of the excess ammonia, but find out where the extra organic material is. These chemical processes use oxygen, the same oxygen your fish need. You might see your fish at the surface gasping for air; in fact, the oxygen might be low in the aquarium, to you might add an air stone during the cloudy phase passes. If you have a new tank with no fish, you can do a water change, stop adding fish food, turn off the lights, and wait till the bloom subsides and the autotrophic bacteria catch up with heterotrophic bacteria that run out of a food source.