A few weeks ago, I set a glass cylinder vase about 3"diameter and 8 or 9 inches tall with a piece of FRP with a 1 1/2" hole drilled in it siliconed to the top. The shrimp I used for bait was eaten on the fourth night. So, I cut a piece of 1/4" Styrofoam about 2" diameter and folded/curved/bent it to get it through the 1 1/2" hole and inside the trap for a one way door.
Since then, I've had no takers. I burned a few holes in the Styrofoam to let the smell out.
I have reagent grade ammonium chloride but haven't been able to bring myself to nuke the tank.