stone/rock crab

[new]

after losing a couple new additions of fish in the same area of tank and chalking it up to shock i saw a crab that hitched into my tank and looks like a small stone crab. was just going to wait until he was to big to big to hide inside the rocks to get him, but now my gramma has apperently fallen victim as well and he has been in the tank for months. any advice on finding and removing this crab?
firgured this out(unfortunately)see my new post.

 

[wolffam]

Try a tall glass. Place at the entrance to the location you think the crab is. Have it tilted slightly. Place some food in the bottom. If all goes well the crab will go into the glass for the food, but will be unable to climb back out. I tried this, but before the crab went into the glass I was able to catch him with the net. Good luck, they are quick!