Donski, how big are the hermits?
Personally, I have not had a lot of success with the hermits we have available in Australia - I tended to end up with a lot of empty snail shells:eek:. I think snails do a much better job of cleaning up algae etc and thus I now have snails and no hermits.
A quick search of a number of sites reveals similar thinking, especially in a reef tank. They can be good for cleaning the sandbed, but this job has been taken over by stromb snails these days.