So I have a 55 gallon that used to have 5 platties in it, 1 male and 5 females. well about a week ago, my male died. so now I have 4 female platties. Yesterday my girlfriend came over with this new fish for me out of nowhere. it was a blue male platty. I thanked her and asked her where she bought it from. she told me she bought it from the local grocery store. I immediately ran to my room and brought old my old 5 gallon plugged int he heater and put in some water that was supposed to go into my 55 later that day. so anyway I added safe start and put this platty in. I am extremely concerned because I would never really buy a fish from a grocery store. how long should I keep him in the 5 gallon to make sure he will not spread any disease to my other fish? as well as it looks like he is missing scales on his head and it runs a straight line between his eyes to his top fin. what is this? is this something to be concerned about? will his scales come back? can I treat it? what should I used to treat this?
