hi so i have these two RTC’s in a 1800 gallon pond with some gar oscar and irredecent’s and i just recently noticed red abrasion marks on both my rtcs none of the other fish seem to be bothered but the rtc’s are seeming more lethargic than usual water parameters are good the bottle just looks a little darker because of the lighting but nitrate is reading just under 20ppm and ammonia under .25ppm water temps stay between 76-86 depending on external temperatures i tried melafix and some other bacterial/ fungal meds and it didn’t do much any ideas on how i can resolve this?
