pond fish sores on head
Two of my pond fish have what looks like sores on their head. The largest and oldest fish has had a discoloration there for over a month I think. The plain orange one for only maybe a week or so that I have noticed. They are both about 8 years old. Both the oldest of the 5 fish in my about 600 gallon pond.
Wonder if this would be a bacterial infection?
I know things aren't done completely properly with my pond. Already this season I have done complete changes in the water 3 times. Wondering if it could be the shock of the change of water from warm to very cold? Also still have my old Pondmaster 2000 underwater filter and when I change the water I see that it is so badly filled with debris, etc.
Maybe that is causing too much bacteria in the water.
Wondering if I should purchase Melafix and add to water or if I should get medicated fish food. Or do both. Any suggestions would be much appreciated.