The way I do it is pull them out and quickly find the weakest spot and snap them like a wishbone.It should snap easily.If you have a tough spot that you really want to frag,I would recommend using a dremel. I would also recommend that you wear gloves..and use your gloved hand to encourage the tentacles to retract before you remove it. They cannot support their tentacles out of water very well. It probably would'nt hurt to wear protective glasses either, their toxin is pretty powerful.{to me it is anyway}You could bring it to the surface in the tank to look at,get an idea where you will frag it...and then take it out..if a couple tentacles get damaged it should'nt hurt it..they are pretty resilient.