My 1 month old tiger oscar went from black and orange to light brown and orange like some sort of coating on him , he is in a 35 gallon tank it has been up for 1 month and just recently got a plco and he lasted 3 days then died so i am thinking it may have died because of what the oscar has , the water temp is 76 and took the water to 3 diffrent pet stores all say water is ok and nitrates are ok to , im new to this aquarium thing so any help would be greatly appreciated.