The reasons of this process are different so as the treatments needed.
Incorrect cleaning + Infusoria
In an anew found tank you may see that within the first 2-3 days the water becomes cloudy as if you dropped a little milk in it. This happens because the tiny unicellular organisms - Infusoria - brought in together with the fish and plants begin to reproduce and grow in number. Treatment: wait for 1-2 weeks till the water gets clear. You can speed up the process by adding some water from a seasoned aquarium. The described event can also happen in a new unpopulated tank. So when it is made ready and the water is poured inside, the better thing to do is to arm oneself with patience and wait with the settling of fish and plants.
Many beginning aquarists try to completely change the water in the small tank during each cleaning. This must not be done for several reasons. First, while removing fish and plants you injure them. Second, you break the so-called biological equilibrium. Very frequently the beginners complain: "The more often I change the water the faster it gets cloudy". And this is true. Normally in the tank different interrelated biological and chemical processes permanently proceed. An enormous amount of water and substrate bacteria digest the products of decay and metabolism and the remains of food. The bacteria are the food for Infusoria, etc. When you change a big amount of water in the tank this provokes a rapid reproduction of saprogenic microorganisms.
A well equipped and well kept aquarium may sustain for years and never need entire change of water due to biological equilibrium. In order to organize a better filtration lay a well washed coarse sand at the bottom of the tank (the dark color is better) in a layer 4-5 cm thick.
Quick growth of bacteria can sometimes be caused by a remained uneaten food and dead parts of aquatic plants. Treatment: clean the substrate with a rubber tube (siphon tube) and top up fresh water, which has the same temperature as the water in the tank (total change is not recommended). Now wait for a while.
Suspended particles in water
The easiest reason of the cloudy water is that the suspended tiny particles of substrate are present in it. This can happen, for example, when you quickly top up water in the aquarium. Such "mist" doesn't bring any negative consequences and in a short time disappears when the particles settle down. Treatment: just wait for a while.
Overpopulation
Normal density of population is 2 to 3 fish sized 3-5 cm per each 1-3 liters. In the overpopulated tank the water sometimes becomes cloudy especially if there is not enough aquatic plants, no aeration or filtration. The accumulated products of metabolism serve as a good nutrition for multiple bacteria and unicellular organisms. They can cause a disease and even a mass death of fish, let alone that such aquarium doesn't look attractive. Treatment: quickly remove extra fish.
Incorrect feeding
The reason of major troubles is incorrect feeding. Refrain from feeding with dried food (flakes, pellets, etc.): fish do not like it much and it can spoil water. Treatment: introduce a proper diet, which consists of live food.
One of the best foods is mosquito larvae. An adult small-sized fish needs 3-5 worms a day.
Watch that any food is eaten within 10-15 minutes and avoid larvae to remain on the bottom of the aquarium. Another good food is tubicid worms. Before each feeding rinse a portion of worms well in clear water.
A real splendid food is phantom midge. This is a transparent floating larva of one of mosquito species. It doesn't dig in the substrate, can live in the tank for long and fish like it much.
At home one can easily raise a culture of another kind of worms - white worms. They are kept in a small box filled with soil.
Some more good foods are daphnia and cyclops. These you can gather in a puddle by means of net, made of fine caprone.
Experienced aquarists also use scrapped fresh meat, though this should be done very carefully, because meat can very quickly lead to a water rot. If the water became cloudy, stop feeding for several days - this will do no harm to fish but the bacteria will perish.
There is a rule: better to underfeed than to overfeed.
Sometimes one has to use a dried food. Treatment: give it in small portions and watch the fish eat it all immediately. Snails can help here a lot, since they readily eat the remains.
Burrowing fishes
Some kinds of fish that dig the substrate can also cause the water clouding. Such blur is harmless. Treatment: add more substrate at the tank bottom.
* Do not change the whole water in the tank
* Watch the food is eaten within 10-15 minutes. The constant presence of food at the bottom of the tank is inadmissible!
* In a new aquarium the water can remain cloudy for several days because of the rapid growth of unicellular organisms
* In an overpopulated tank the water may become cloudy, especially if there are few aquatic plants, no aeration and filtration
Translated by Tatiana Karpova (Moscow)
(MSU, Biology faculture, Dep. zoology and ecology).