Had two crabs and don't think they did a thing.
I'm another with luck with manual removal. Some around the tank doesn't bother me but every once and a while, I'll break loose all I can reach with a dental pick and net it out (just hold the net in front of the return) and let the rest go down to the filter sock. Probably been about 3 months since did it last and need to get right up to the tank to spot any.
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