Unfortunately the crab won't help. And you probably are only seeing the beginning of dead fish. Has this tank only been running for 2 weeks? Thats alot of fish in there to "start" a tank. You are now probablt finding out that this way was not the best way to do it.
If it is possible, you should take the fish out of the tank and back to the LFS
and do a non-fish cycle of your tank. Sometimes this is not possible. Damsels are pretty hardy fish and most will probably survive the cycle but the stress will be very much for them.
What are you water parameters now? Ammonia, Nitrite, and Nitrate?
Maybe we can help you through this with out much loss. The folks here are good. They know alot. You will probably hear some things you may not like but it will be for the good of the fish and youself if you intend to stay in this hobby.
125 Gal-35 Gal Wet/Dry-Tetra-Tec PF500 HOB
(3) AuquaClear 301 Powerheads-600 GPH
Automatic Tempature Controller
5-6 Inch Sand Bed-200+ lbs of LR