If you have had them in there for a week and you aren't getting any ammonia readings you might have skipped the ammonia phase of the cycle already. I wouldn't worry about having a LFS double check. If food is going in then ammonia is being produced. You may also not see any indication of nitrites as they are quickly converted into nitrate. The live rock may also be converting your nitrates into nitrogen gas through the anaerobic that are on the rocks, so you may not get a nitrate reading. Although if you don't get a nitrate reading I would suspect the test kit and you should double check. Give it another month or so before you do anything to the tank and let the bacteria levels stabilize and the dead rock start to seed and such. Then you may want to remove the damsels as they will become real pains later and will kill or hurt most things introduced to your 75. Remember that patience is the best policy and nothing good in this hobby happens fast.
