I worded that wrong. The tank becomes cloudy because the heterotrophic bacteria becomes free floating. They become free floating due to an abundance of waste that they feed on is still in the main tank probably in the substrate.
This sounds like a bacterial bloom to me. I'm not sure what waste heterotrophic are feeding on. Urine (which is virtually all the waste that fish produce) is ~ 2% carbon from a molecular weight. (Urea is ~2.9% percent of the urine, the other 97.1% being hydrogen, oxygen, chloride, sodium, and potassium. And urea is almost exclusively hydrogen, nitrogen, and oxygen, with only one out of the 8 atoms being carbon.)
And fish waste on the other hand contains no carbon at all according to this study:
http://papercranemarketing.com/AquacultureCentre/files/research-publications/Chemical Composition of Trout Manure.PDF
Most of the carbon is in the food.
Grain is 45% carbon. Proteins are made up of amino acids and all amino acids require carbon.
Carbohydrates and lipids (fats) are chemical structures made up of carbon, hydrogen and oxygen. Heterotrphic bacteria would seem to prefer fish food (protein, grains, lipids, carbs) not urine as a food source.
If excess waste---which means urine or manure---is the cause of bacterial blooms, then it seems everyone with nigh ammonia should have a bacterial bloom.
Over feeding, so it's thought, is the main cause of a bacterial bloom in an established tank.