Did you dechlorinate the new water before adding it to the tank?
How are the other fishes reacting?
Add a double dose of dechlorinater to the tank and increase aeration/ surface turbulence.
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You need some sand or fine gravel on the bottom so the fish can't see their reflection and feel more comfortable.
Pictus catfish can reach 8 inches in length, need to be in groups of at least 6 and eat small fish. If the fish recover, maybe return it to the shop and get something more appropriate.