Works fine, depends on the nem though, they can crawl out if they really want to. They get covered by algae only as fast as the rest of your tank does, so I didn't have too much trouble. Flow inside the cup isn't great, so detritus can accumulate depending on how large the nem is so you just have to take a baster or coral feeder and blow it out every now and then. Overall, I like them and have used them to hold BTA splits before sale or to grow out.