Few things can be more sad and disappointing than the disappearance of fish without a trace. The fish is there at night and is missing when you check the next morning.
Fish can disappear for a variety of reasons. Some fish jump out of the water. Jumping out of the water can be caused by poor water quality or overcrowding.
If you cannot find this fish, it is necessary to do a proper search in the tank. Sometimes, fish which are sick may hiding in a corner or crevice. You can treat the fish if you locate it.
Sometimes, fish die due to natural reasons and they are eaten by the other fish in the tanks.
In some other cases, fish die behind plants or other accessories such as filters. It will be difficult to detect them in such cases.
Some times, fish which have disappeared will reappear in a few days. They may have been hiding somewhere or may have been sick.
If there are frequent fish disappearances, you may have to suspect another fish. Some fish may swallow or attack other fish. You must identify such fish and remove it from the aquarium before adding new fish.