Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Cloudy water can be caused by several things.
Ammonia. Though I usually see the bubbles first- bubbles lingering at the surface, not popping.
Disturbing the substrate. For example, when you are filling the tank.
Heterotrophic bacteria. These are not the nitrifying bacteria. They feed on dead things, such as fallen leaves and other things. When the food is gone the population drops, and the water clears up.
pH or mineral issues. Can happen when you are altering the pH in some way. Example: ADA soils remove the carbonates from the water, and this allows the pH to drop. I have not seen cloudy water from this, though. Usually it is the other way: When I add something to raise the mineral levels and pH for certain fish the water is cloudy until the minerals are fully dissolved.
Beginnings of green water algae. Looks white or grey at first. If you have some white floss (polyester quilt batting or similar) you might be able to see the color of whatever it is. Green = algae. Same color as substrate = substrate.