The newly changed water in the fish tank turns white and fog, indicating that the nitrification system in the tank has collapsed. Nitrification system is an essential part of fish tank, which is mainly responsible for absorbing ammonia nitrogen produced by microbial decomposition and converting it into nitrate. Without nitrification system, the water body will become turbid after a large number of microorganisms multiply, and at the same time it will cause poison to fish. Therefore, in this case, it is necessary to re-raise water and cultivate nitrifying bacteria.

1. Change water regularly: To improve water quality, the first thing to do is to change water. Usually, there is no fixed period for water change, and the frequency of water change should be determined according to the maintenance of water quality. If the water quality deteriorates rapidly, it should be changed once every three to five days. If there is a filtration system, it can be changed once a week or two, and about a quarter of it can be changed every time.

2. Strengthen filtration: If there is filtration equipment in the fish tank, the water quality can be better maintained. If the filtration effect is not good enough, the filtration can be strengthened by increasing the power of the filtration equipment and cleaning the filter cotton. Sufficient filter materials need to be put into the filter box, so that the filtering effect can be guaranteed.

3. Reduce feeding: In the daily feeding process, feeding must be well controlled. If too much food is fed and fish can't eat it, a large amount of food decomposition will also lead to water deterioration. Usually, it can be fed three times a day, and it is necessary to ensure that the fish are eaten up within 3-5 minutes after each feeding.