What medication should I use? Please help.

[ikan]

My ancistrus grow out tank has been infected by disease in the last 6 weeks and still no sign of getting better. I have lost so many fish I don't even bother to count them anymore.
I have tried tetracycline, ti-sulfa, melafix, broad spectrum and white spot medication in vain.
Before they died some had open wound/exposed flesh other had fungus that looks like cotton wool.
What should I try next, I am getting pretty desperate now.
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Details
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Temperature 26.5 C
PH 7.5
GH and KH unknown
Ammonia, Nitrate, Nitrite basically nil
Water change frequency varied from 1 - 5 times/week at least 30%

Tank setup 3'x18"x18"
Subtrate None
Filtration Cannister filter eheim 2217 1000ltr/hour
Furnishing Drift wood and java fern
Other tank mates: 1 Ram, 1 praecock rainbow
Last fish added 1 year +

Symptoms:
First started with 1 large ancistrus with bad case of fungus growing on it's mouth. I removed the fungus and salt dip. It recovered. Then few younger ones showed the same simptoms and few started to die. Can't possibly check every single of them for fungus, some fish are/were only 2 cm long.

Treatments:
I added tetracycline (full doze) and melafix. This medication continued for 1 1/2 week and fish continued to die. I did water changes 3 times/week.
I then did a big 90% water change and started a trisulfa medication and did water change almost daily for 1 week but fish continued to die and fungus also grew on the body/skin.
I did another 90% water change and added trisulfa and white spot medication (0.85g/l malachite green, 98g/l formadehyde). I increased the temperature to 31 C for 1 week. Fish continued to die and fungus still infecting fish. I think the white spot medication didn't agree with ancistrus and I lost 13 fish in 1 day.
I did another 90% water change and treated the tank with melafix daily as recommended and I didn't do water change for 1 week and left the temperature at 31 C.
Fish continued to die.
This morning I did another 90% water change and dropped the temperature to 26.5 C and added fungus & finrot remedy (2.0mg/ml acriflavine, 0.4mg/ml malachite green)

[Barbie]

Daily water changes are never a bad place to start. At the top of this forum is a post that details what information we need in order to make informed guesses into how to help you. Please add that information to your post. Thanks!

Barbie

[ikan]

Thanks for the info Barbie. The details has been added.