I had to do something similar the other day and found I had to *trick* the sucker. :) I put an algae tablet in a wide mouthed pint jar and put it on it's side in the tank and just waited a while. It finally came to the bait several times and beat me back out. I finally put the net over the open end of the jar quick as I could and ended up with the critter in the net. Peggy Mitchell