Something is nipping my fishes tails

[phar]

So I've noticed that a few of my fish are missing parts of their tails. In the last week I'll go to bed and wake up and a little nip is gone.
During the day, there is no fighting and they all seem to get along. The only thing I could think of is a really aggressive female tomato clown. (I have a pair.)
My live rock has no pests. I have one medium hermit crab. (No bigger than a quarter at the most.) Could the crab be nipping their tails at night?
Any ideas as to what it could be?
Here's the fish I have in my tank:
Small Bariene Tang (Nipped tail this morning...One of his streamers is missing)
Small Yellow Tang
Small Multicolour Angel (Badly nipped tail.)
Pair of tomato clowns
3 green chromis
lawn mower
Various LPS and SPS.
Thanks,
Patrick

[Madreefer]

I'm betting on the tomato clown. They get very territorial if another fish comes around their "spot" such as an anemone. At least thats what i've seen in my old tanks.

[RuGlu6]

Are you sure your LR has no pests?
Yo might have bobbit worm aka Eunice worm. The stay small for a while and after a while just explode in size.
The only way to be sure that you don't have one is when you started with Dry Rock not Live Rock.
If you did start you tank tank with dry rock the you can bet on the clown.
But you don't see anything during the day and that can be something you don't know about that hiding in you tank's dark corner.