I have a 8 inch oscar, and two large severums that have all gotten hole in the head. There in a 110 gallon fish tank with a fluval 404 canister filter. I do a weekly 25 percent or more water change. I took the carbon out of my filter about 2 weeks ago and nuked the tank with metranadizole this seems to have had little to no effect on the fish's disease it still seems to be progressing. I tested my water and my ph was 6.6 and my water hardness was 0-1 dkh. I was wondering what the dkh for an oscar should be as my carbonate hardness seems to be the only water parimeter that is off in my fish tank. Also is there anything else anyone can think of that I should try. I should also add the fish are fed a very diverse diet and I do not suspect diet is the problem.

in order to help you effectively we need to have the rest of your water parameters ie : ammonia nitrite and nitrate.... prestine water is the first and foremost defense and cure for hole in head

I have been looking around at various websites and most of them state that Oscar's like soft to hard water. Really, this doesn't really help your situation at all. I think you have fairly soft water so you should be okay and I don't think this is the cause of your problem. I would go along with what Bent has suggested, provide us with some information on your water quality. There must be something wrong somewhere if all of your fish are being affected

BentBarrel wrote:

i concur with Bent. and i was surprised that you did medication without checking
the water parameter first. medication is useless if you have high ammonia, nitrite,
and nitrate. pH is not much concern as long as it is stable.