The built-in filter in the fish tank is relatively not good. Usually, this kind of filter is self-contained in the finished fish tank, which can meet the simple filtration, but once the feeding density is high, the filtration effect can't keep up, and because it is integrated, sometimes it can't be changed if you want to. Therefore, it is usually not recommended to buy fish tanks with filters, and it is best to match filters independently, so that appropriate filtering equipment can be selected according to the situation.

1. Filter cotton: Filter cotton is an essential filter material in filtration equipment. Its main function is to filter out large particles of impurities in water and achieve the effect of physical filtration. In order to ensure its filtration efficiency, it should be cleaned every once in a while, but it must be washed with the original tank water, otherwise it will destroy the nitrifying bacteria on it.

2. Activated carbon: Activated carbon is a filter material for chemical filtration. Its function is to absorb ions in water, thus preventing fish from being poisoned. Like other chemical filter materials, its adsorption capacity has an upper limit, which should be replaced in time after reaching the upper limit, usually every three months.

3. Bacterial house: Bacterial house mainly provides a place for nitrifying bacteria to attach, and it does not participate in filtration itself. However, after establishing nitrification system, it can improve water environment and reduce ammonia nitrogen content in water, which is of great help to water quality and fish health.