Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Tell us more about your tank:
How long has it been set up? Is it cycled?
What is in the tank? Plants? Fish? Shrimp? Other?
What are the water test results? Are these results pretty much normal for this tank or has something changed?
What sort of additives do you add? (Dechlor, plant fertilizer, pH adjuster...)
Cloudy water can be from any of several issues, here are a few ideas:
Hetertrophic bacteria can grow so fast they cloud the water. Mostly they feed on dead matter, such as fallen food. You can continue what you are doing, vacuuming the tank to remove whatever might be feeding these bacteria. UV might kill the bacteria, but they will only grow right back as long as there is a food source. They are all around, and will land in the tank from the air and anything that goes into the tank. Try to find and stop the source of their food. Are you feeding the fish too much? Is this a new tank with garden soil as a substrate? Did your children dump something in the tank?
Try feeding just 1/4 of the regular amount. Normally these bacteria live in the tank, decomposing things, but their population is stable, and this does not cloud the water. When there is an increase in their food supply they multiply really fast.
If you are also having problems with ammonia or nitrite, then adding Nitrospira species of bacteria (the real cycle bacteria) will help. Otherwise, not. It is not bad to add these bacteria, but if there is nothing for them to eat they will just die. All other 'cycle bacteria in a bottle' products are a waste of money. Wrong bacteria.
The few times I have had ammonia problems the tank has been just a bit hazy. Not much (but then the ammonia had not gone up much). Definitely monitor the ammonia. If it is ammonia, then keep up the water changes and try to find the dead fish or whatever is contributing to the problem.
Trying to alter the pH can lead to cloudy water. If you are trying to do this, then please give us all the details: GH, KH, pH of tap and tank. Why you want to monkey around with the pH.
Some decorations can do this. Rocks that are high in calcium or magnesium carbonates are usually the ones that do this, but I have heard of other things that react with the water and the water gets cloudy.