Hey so i have Comets in 2 different tanks they came from the same place (bait store) and last few days 1 fish from both tanks have started getting a lot of black spots. what i have read is that it might be ammonia burn? but 1 out of 10 has it in my 45 gal aquarium and 1 out of 40 in the 250gal FT. a little help?