It will stay in the tank. I'm not sure how they reproduce but if you have just one and don't over feed your tank like crazy, as stated in earlier posts, this is a good member of your cuc. If you oversees your tank, I have seen threads on here where they get huge and then they might bean issue for your livestock.
I have one that I have seen in the daylight. Pretty small, maybe a inch. Have never seen him again. There are some livestock that you can get to keep them under control. Various wrasses, arrow crab etc.