My fish have been in the same tank for about 18 months then I added some smaller comets 4 Why are goldfish eating fantails tail How can stop them their tails?

There are a few reasons why goldfish may be eating the tails of fantail goldfish:

Overcrowding: If the tank is overcrowded, the goldfish may be stressed and more likely to engage in aggressive behavior.

Competition for food: If there is not enough food for all of the goldfish, the goldfish may compete for food and eat the tails of the fantail goldfish.

Boredom: If the goldfish are bored, they may start to nip at the tails of the fantail goldfish as a form of entertainment.

Poor water quality: Poor water quality can stress the goldfish and make them more likely to engage in aggressive behavior.

To stop the goldfish from eating the fantails' tails, you can try the following:

Reduce overcrowding: If the tank is overcrowded, you should remove some of the goldfish and put them in a separate tank.

Increase the amount of food: If the goldfish are competing for food, you should increase the amount of food you are giving them.

Provide more hiding places: If the goldfish are bored, you should provide more hiding places for them.

Improve water quality: You should regularly test the water quality and make sure that it is within the ideal range for goldfish.

If the goldfish continue to eat the tails of the fantail goldfish, you may need to take more drastic measures, such as separating the goldfish or rehoming them.