2/3 of my Goldfish are hurt, what's going on?
(Chagrin Falls Ohio, United States)
2/3 of my goldfish have some of their tails missing.
The one who doesn't is constantly on the bottom of the fish tank.
What's going on with my goldfish?
This sounds like tail rot to me.
I am assuming that your Goldfish are by themselves and there are no other species of fish with them. Many tropical fish like to munch on the long-flowing fins of Goldfish.
Tail rot is brought on by poor diet, poor water conditions or both.
It is caused by bacteria that are always present in water which attack any fish that has had its immune system weakened.
The fish sitting on the bottom is just exhibiting different symptoms of the problem.
You need to act quickly, but the solution is easy.
Do a half water change immediately and add some non-iodized cooking salt to the water. For a 15 gallon aquarium I would add about a handful.
The fish should ideally be moved to a sickbay filled with clean fresh de-chlorinated water. That alone will start the recovery process.
Feed the fish live foods to speed up recovery.
If a lot of damage has been done to the tail fins it can take up to a year for the fins to fully grow back.
Go to the website page on tail rot disease
which gives some treatment options.