Lowering the SG in your main tank to the levels required (1.009) will kill everything in your tank except your fish. Snails, crabs, corals... everything. That's why you do it in a quarantine tank. Lowering the SG even to 1.020 quickly in your main tank may have started the beginning of the end for your crabs/snails, and yellow polyps. They may not be dead right now, but they sure aren't very happy with you, and may not be doing too well in a week or two.