I had a similar problem with crabs when I first cycled my tank and there's still a baby one in there that I haven't managed to catch yet. The glass trick works wonders but if it's a swimmer crab (paddle shaped rear legs) then it'll simply swim out of the glass again, so you'll need a different plan of attack. I was lucky with first ones, managed to net them by chance.
I'm yet to try it on this one (as I'm working long hours and too knackered at night to bother at the moment lol), but you could go fishing... Tie a bit of bait to some string and wait patiently for a catch, probably best at night though.
Good luck either way.
Looking good, but hold off on more fish right now and remember the reefers saying "nothing good happens fast in reef aquariums"