My advice would be to get a test kit for ammonia, nitrites and nitrates
a.s.a.p and check your water parameters. Ammonia should be at 0, nitrites at
0 and nitrates under 20 if your tank is fully cycled and healthy. You
mention that you have recently cleaned your filter. Did you clean it with
tap water or with old tank water? Cleaning filters under tap water would
have killed off your beneficial bacteria so causing water quality problems
which could be why your fish is under the weather. As long as you get your
water quality perfect the fish with missing scales should heal well and
quickly. If the water quality isn't very good and without test kits you can
have no idea about this, then other problems such as fungus etc could occur.
Mel.

"Dee" wrote in message
...

"Geezer From The Freezer" wrote in message
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Dee

What are the water parameters like? Ammonia, Nitrite and Nitrates??
Are you over feeding it? How long has your boy/f been away?
When was the last time a water change was performed?

1/3 water changed 3 days ago. Water is clear and clean, filter has been
cleaned out, sorry no idea of nitrate etc but I've added nothing different
than what the fish have been in for the last 9 months. Only feeding a
pinch
of flake food twice a day. Other fish seems fine but the black one has
lost
some of his scales near his top fin and near his eye where is was caught
under the air stone. When fed he swims around the tank as he always has
but
when the food's gone he just sits on the bottom. He wasn't doing that
yesterday