First I got a question.
What meds have you treated with ?
What are the other tank mates? and is there nipping going on?
Oscars can be a bit nippy when in breeding and will at times fight each other off the nesting spot. Causing a wound to take on a secondary infection. which I will explain further down.
3 types of medications
I tell all my fisie friends NEVER to over medicate. This can do more harm than good. Not to mention what it does the the water chemistry. I really hate to recomend any method of treatment NOT knowing what was used.
Now what I would reccomend would be to use ( Maracide ) this is a product from Mardel Lab. which is VERY affective against many external fresh water parasites as well as many fungus infections.
This can be bought at most pet stores and it is a 5 day treatment. Though I would NOT use it till we know what you have used already. Over medicating can make matters worse before they get better. And in some casses can prove to be a fatal mistake. Again ,
all depending on what has been used.
Alot of times some simple
aquarium salt will help some types of fungus.
If Maracide is used I suggest the whole 5 day treatment. 1 drop per galon of water so I would suggest using a smaller tank for medication. Remove carbon (if any) as to this will make meds less affective. After the 5 day treatment do a 20% water change and add new carbon if used. If the existing carbon ( if any ) is old it can remain in the filter as to this will have little affect on medication. ONLY if carbon is old. If NOT remove carbon.
The water may turn a shade of green while the tank is in medication. Though this can be removed once treatment is complete with some freash activated carbon. AGAIN PLEASE DO NOT USE till we know what else you have used.
Still with me?
There are several types of fungus with can bring on what you are discribing. Could be a wound / bite from a tank mate or mate that took a turn for the worst. Many open sores if let untreated and tank conditions are right will cause a secondary infection. In some casses this may look like white slime / cotton . Not saying this can be the problem though just an example of the many things that can be wrong.
Alright I will keep checking back after dinner. Time to feed the gut.
Hope this helps.....
Sorry about the short reply but I just got home and need a few to unwind and feed the zoo. 60 tanks - 3 Florida cooters (turtles)- 1 aligator snapper (turtle) - 2 painted box turtles - 1 dog - 2 cats - 4 kids - and 1 girlfriend. O, wait them aint part of the zoo. Or are they...
Alright better go before I get in trouble.
Danny
too late yikes....