Hello I had this problem a few weeks ago.
you dont mention the kind of fish you want to remove but mine were large gobys and so a nightmare to catch. I used a trick I learnt when surveying for newts in the wild, TRAP THEM.
Depending on the size of the fish use a clear plastic water bottle (clean). Cut off the top funnel section and widen the entrance so the fish can swim in, then invert the funnel into the bottle so it points to the base of the bottle. Cut a few small holes in the bottle to let the air out, put some gravel in to act as ballast and pop a couple of worms or blood worm in the bottle and leave overnight. (make sure small air bubble is trapped inside if you have any corys in the tank!)
The fish will swim in after the bait and will not be able to get out! I hope that helps and good luck
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