Can anybody advise on the best way of eliminating these from a reef aquarium setup, my local shop has said that there are crabs and fish will eat these critters
Any particular reason you want them gone?? Other than a very small number of species (out of over a thousand), they are pretty much considered harmless and good members of your CUC.
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Wanna calculate the cost of that new reef tank?? Take your worst nightmare, double it, and you're halfway there.