Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
In an aquarium there can be several causes for cloudy water. Cloudy water is not generally in itself toxic to the fish, but the reasons may point to some conditions that may become toxic.
1) pH or water hardness issues. Changing the pH is a tricky thing to do, and pet stores are all too ready to sell you pH Up and pH Down sorts of products without helping you understand what you are trying to do or to even hint that there is anything complex about water chemistry. If you think you need to alter the pH of your water please post:
-Tap water pH right out of the tap, and tap water pH after sitting out for 24-48 hours.
-Tap water GH and KH.
-The species of fish you are interested in keeping, and if you want to breed this fish.
This sort of problem can also show up if the water company changes the composition of the water, for example if they get their water from more than one source.
Another way that pH can be altered to the point of causing cloudy water in a tank is if some decorative rock or substrate is a rather soft form of limestone and the water is slightly acidic. This can be tested by putting the rock or gravel in a clear glass of tap water and testing the pH, GH and KH over several days or a week. You can see the water clouding up in a clear glass, and you can monitor the water chemistry changes.
2) Ammonia, especially from dead matter such as dead fish or snails, fallen food or similar source.
The cure for this one is to do enough water changes to keep the ammonia under .25 ppm, the nitrite under 1.0 ppm, and nitrate under 20 ppm. As you are doing these water changes vacuum the substrate well to remove fallen food and other debris. Feed less, so the fish clean up the food right away, and skip a day’s feeding once a week. This problem should go away when the tank is fully cycled, and when you find the dead fish or whatever is contributing to the steep rise in ammonia.
3) Pretty much every form of substrate (sand, gravel, planting soils) have fines in them, even a graded product like pool filter sand or gravel. The tank can get cloudy from the dust if you stir up the substrate when you were moving a decoration or planting. Or did not wash the substrate before using it. Or poured the water in so fast when you were filling the tank that it stirred up the substrate. Usually this sort of cloudiness will settle in several hours to a day or so. If you do a water change and deliberately stir the gravel or sand so there is more dust in the water then remove this water with the water change then there is less dust overall in the tank, though the water may be cloudy with the debris that you have not removed. Cichids and some other fish are notorious diggers, and will keep clouding the tank this way. If you have a bad substrate that keeps clouding the water change it for something that does not. (Or has a lot less dust to begin with. The filter will gradually remove whatever the fish stirs up)
4) Heterotrophic bacteria will grow wherever there is food. These species can grow fast enough to cloud the water. They are feeding on organic matter that might have gotten in the tank while you were setting it up, for example your own skin cells and oils. Usually these bacteria settle down within a few days to a week, These are not nitrifying bacteria, but are beneficial. They are usually triggered by a new set up, or some change that has provided more food for them.
5) Green water algae will begin growing looking like white or grey cloudy water before it turns green enough for you to see that it is algae. If you have any white polyester floss in your filter this might show green before the tank water looks green. If you have no live plants you can turn off the tank light and hope the green water algae dies, and there are other things you can do without buying algaecides.
6) Other: Someone put something in the water: Cheerios, Jell-O, paper or cardboard, all the fish food you just bought…