Oh - it shouldn't be a film, because that is glass on the top - the water literally goes all the way to the top (it's a fluval edge)
There are bubbles getting trapped at the top from the sponge filter though - maybe that's what you are seeing? I used to have the flow higher but they weren't nearly as active and social with each other. I think I could get away with increasing it a little though
About the tankmates - they actually aren't going to be around long lol - the crabs are going to a new home as soon as a seahorse gets pregnant (I don't have another tank for them to go to, so I'm going to donate them to my LFS) - The peppermint shrimp generally stays in his rock, but if he starts getting out and bugging them, I'll donate him too. I'd like them to get a chance to eat any possible aiptasia left that I can't see or anything else in the rock.