If you have 3 black molly fish but 1 has disappeared think it was ill is possible that died and the other 2 ate still there yesterday so seems weird went quickly?

There are several possible reasons why one of your black molly fish may have disappeared and the other two may have eaten it.

1. Illness: If the missing fish was ill, it may have been weakened and unable to compete for food or defend itself against the other fish. As a result, the other fish may have attacked and eaten it.

2. Aggression: Mollies are generally peaceful fish, but they can sometimes be aggressive towards each other, especially if they are overcrowded or if there are not enough hiding places. If the missing fish was being bullied by the other two, it may have been stressed and more susceptible to illness or attack.

3. Water quality: Poor water quality can also stress fish and make them more susceptible to disease. If the water in your tank was not clean or if there were too many fish in the tank, it may have contributed to the missing fish's death.

4. Cannibalism: Mollies are known to be cannibals, and they may eat their own young or injured fish. If the missing fish was small or weak, it may have been eaten by the other two fish.

It is difficult to say for certain what happened to your missing fish, but these are some of the most likely possibilities. To prevent a similar incident from happening in the future, you should ensure that your tank is properly sized for the number of fish you have, that the water quality is good, and that there are enough hiding places for the fish.