Unknown Discus Disease

Hi,

I am new to this forum but i was really hoping that someone could help me diagnose my fish. It has been sick for almost two years. Over this period i have treated it with metronidazole (as a bath and in food) and praziquantel (within food). Nothing seems to have worked except for the metronidazole which cured hole in the head (this poor fish has been through everything), but that only lasted for a very short period of time.

His gill activity seems fine with no extreme fanning and a relatively constant breathing rate.

However he does head stand almost all the time or at the very least swims at an angle. This kind of behaviour started after the first isolated metronidazole treatment.

Changes colour rapidly from relatively bright to almost black. When feeding colours up momentarily and returns to stressed colours as soon as fed.

Tank size: 6*2*2, small sump and 2 canister filters, turnover is approximately 5000l/h

Tank mates: 5 other discus, four large angels, 15 bristlenose, large ghost knife, large pleco, a couple of tetras.

i thinks its coped an internal infection that has permenantly damaged the swim bladder.

the metro would have stoped the infection but the damage is permenant, due to the fish having trouble swimming propperly id assume it also has problems eating and as a result is just "weak".

looking at the fish it is stunted. all you can do is just keep it as best you can but it will never be 100%

best thing for all your fish is to keep your nitrates below 10-20ppm (i keep mine under 5) but that could be hard in a planted tank.

2 years?
I'd of put it out of its misery by now.