Sick goldfish, how to treat?

I have a 5ft tropical fish tank which used to house four medium gourami's, a cat fish and an 11 year old goldfish.

About two weeks ago the gouramis all suddenly died within days of each other, I noticed small red patches on their scales.

The goldfish, which has lived happily in this tank, now has quite a deep wound near his dorsal fin, about 1/2 inch across.

I have treated the tank with a formula to treat bacterial infections but have seen no improvement in the last two weeks.

My knowledge on fish is limited to a National Diploma in Animal Management which consisted of one semester of aquatic management.

I have tested my water for ammonia, nitrites, nitrate and ph levels with a proper tropical tank water test kit but I have run out of what this problem could be.

Any help or guidance would be much appreciated as I do not want to loose my goldfish with him been the age he is, if I can help find a solution.

I know goldfish should not be kept with other fish but mine has lived in there all his life. I am also aware about putting fancy goldfish with goldfish such as comets but that was not what my question asked.
The treatment I used was from the pet shop.

Becky N, I'm saddened by how insensitive people have been for you. I had a gold fish that I got in kindergarten, for many, many years and I can relate. I named mine Fred. Fred got so big he would move gravel around and night and wake me up. Anyway, here are some ideas, and I hope somebody with more knowledge answers too:

Sounds like you are testing well, but are your test chemicals fresh? They usually only last about a year, before buying new one, take a sample of water to a good fish store that will test it for you. Does the water smell ok? I'm thinking its something in the water (like ammonia.)

Treating a sick fish in the tank can sometimes make a bunch of problems, as it kills off the nitrification bacteria. You might want to add a product like 'cycle' to help restore the bacteria.

You said you treated for bacteria, what about a fungicide? You might want to try a fungicide dip. Especially as fungus can be a problem for a wounded fish.

I would do a partial water change every day or so for a while. You don't want to shock him, but fresh water might dilute what ever is wrong in the tank and help him feel better.

I would also add or change the carbon. Carbon will absorb all sorts of things, and if something in the water, or something that fell into the water it may help reduce it.

Have you figured out what might have caused the wound? Has something gotten in there, or something fallen near the top, or something else that he can scratch himself on?

This is a long shot, but how are you pumps? Is the water circulating ok? On a behind the scenes tour of the Scripts Aquarium, they made a big deal about pump pressure. They have all output from the pumps to a bucket that then flowed into the tanks. Like a little waterfall. They had to do this cause the pressure from the pumps will put too much air in the water, and the fish might suffer hemorrhages (like when a diver get the bens.)

Also, if the water isn't circulating properly, the filters can't do their job.

It really sounds like ammonia burn, and there is a link at the bottom.

Anyway, I hope this helps and I added to as a contact cause I want to hear when Goldy gets better!

Goldfish should not be kept with any other type of fish except goldfish and even then only fancy goldfish should be kept with fancy goldfish. Comets should not be kept with fancy goldfish for example.

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There is no sense trying to treat anything when you are creating the situation which is causing the problem in the first place. The first thing you need to do is fix the reason for why your goldfish is wounded and why your other fish are dying.

After that then you can treat your goldfish otherwise if you don't fix the situation it's useless.

I had a fish with almost this exact problem die about a week ago. He was 7. :(

THE LOOOORD HATES GOLDFISH!

Buy some medicine or medicine food or anything for the fish a from a pet store like PETCO or check what your feeding him

sorry but that goldfish is pretty dam old i say u put it out of its suffering