To kick off I ordered C. aeneus, C. rabauti and some C. similis, 6 specimens of each. The C. aeneus are fine and spawned within 24 hrs of being added to thier new tank. I dedcided to quarantine the C. rabauti & similis as they were quite small and skinny. Now I've noticed that some of the similis have what I can only describe as fungus-looking "tufts" on their fins, and one specimen seems to have it on the body also. I've seen this before on Corydoras in shops but have no idea what it is. Any suggestions as to diagnosis and treatment?
They're in a 75Ltr quarantine tank, no substrate, 2 x large sponge filters (cycled in another tank for this purpose) and some driftwood as cover. Water parameters are pH 7, GH 100 (I can't test TDS or KH at the moment), no detectable NH3 or NO2. Temp 25.3 degrees celcius. I'm changing about 15Ltrs a day and replacing with water of the same parameters and temp.
Also a couple of specimens arrived with eroded barbels which have rapidly started to repair over the past 3 days. All the fish are eating, and generally swimming around and acting normal, none of them seem listless or anything like that.
I've added a small amount of an anti-fungal treatment to the tank, but I'm not sure what the actual problem is...

Thanks in advance,
Shaun