I've had a tank with just your normal goldfish for around a year. There were a few teething problems, some down to the centre not informing me on how to take care of the fish properly. But now i am sure i have got it right.
Half water change every 2 weeks
filter change every 6 weeks (biological filter)
feed the fish once day
the tank has the air pump
but somehow my fish have managed to get an infection. I havent introduced any new fish into the tank for about half a year. At the begining of December one of my fish had an infection. I treated the water with Furlanol, he seemed to get better but unforturnately died a week later
Now one of my other fish seems to have developed the same problem. Its like a growth the scales come away and looks like its going to explode. I have put the treatment back into the water, he seems fine in himself his behaviour hasn't changed but there is obviously something wrong.
i could really do with some advice i dont want to keep killing my fish