Blue Legged Hermit Crabs and Acropora?

So I have three acropora pieces at the moment, and have around 12 blue legged hermit crabs.

They seem to spend their whole time on my acropora corals, I've watched them for a bit, they don't seem to be eating it, however one acro piece is currently looking very bad, so they've now all moved onto my favourite purple one. I am now suspecting that they could be eating my acro ....

So do Blue legged hermits tend to pick on SPS? I have a fair few other corals in the tank and they're completely ignorning them. They are ignoring my Pavona coral however and it sits between the two pieces they're currently at.

So should I get rid of them? They have already destroyed one piece (I think it's pretty much gone, there's little no no visible polyps anymore) and I don't want my second one to be destroyed too - it does have a protector crab, I'm hoping it may actually do it's job.

A €55 coral is worth more to me than the hermits.

Does anyone know any other hermit crabs who actually 'are' reef safe? Red leggeds from my own experience love soft corals!

Tank: 80gallon SPS/LPS reef with some soft corals. 150watt metal halide with 55watt T5 dual tubes lighting. 30gallon sump with working refugium, TMC V2skim 400 skimmer, two heaters (150w and 200w), 3500lph return pump. Tank has two powerheads korlia 4 and nano, 30KG live rock, 20KG live sand with 10KG coral sand mixed.