I have kept shubunkin goldfish for years, but this is my first year with a set of fantails. In my 30 Gallon, with two dojo loaches, two fantails and three shubunkins, the larger female fantail developed a large red lump on her side. I treated the tank with Tank Buddies fungis clear. After three days, I treated the water for ammonia, and the lump became a large patchy ulcer within a few days. She died, and I did a water change, but now my smaller fantail female has a red lump just under her dorsal fin. I assume that I should treat with antibiotics, but I never have before, and I don't want to cause any more damage. This is my first unexplained illness. Please instruct.
Thanks, Crissi Parry

Greetings and welcome to the board!

Sorry to hear your fishies are ill.

One thing that will help us out is asnwering the questions
in the big red box at the top of the page. If you don't
have a water testing kit, take a water sample to your
local fish store. Most places test for free. Make sure
to write down actual numbers, don't get OK or good.

From reading your description, it sounds like your
tank is overstocked. Fancy goldfish(fantails,
orandas,etc.) need a minimum of10 gallons of water per
fish. Narrow bodied goldies (commons, comets, shubunkins
etc.) need a minimum of 15-20 gallons of water per fish.

Filtration for a 30 gallon tank should be 10x the amount of
water in the tank. So, you would need to be filtering 300
gallons of water per hour (300 gph).

Post back with the results and we'll see what can be done
to correct your problem.

I agree with pm. Your tank has too many fish in it. What kind of filter do you have? do you have air stones or bubble walls?

-I have had my 2 fantails for 2 years, but they never had ulcers...however a few months ago, one of them developed red spots on his tail, so i immediately did about a 40% water change and started treating with melafix and salt. The spots went away in a few days.
-I hope your fish get better soon! you might want to think of getting a bigger tank, or a seperate tank to put some of the fish in so they aren't over crowded.