Newbie here. Need crab advice

[Brettdis]

So tonight we saw something new in our tank. It’s been up and running for about 3 months. We got 3 snails 3 blue damsels and 1 shrimp. The light was off. We were gone all day. Turned it on and something moving quickly across a live rock. It tucked into a hole in the rock. If we hadn’t seem it moving we would never know its there. We turned the light back off and after a little bit it slowly started coming back out. I tried to get a pic but impossible without light. As soon as we shine a light it tucks back into the live rock. We tried to catch it but its way to quick. It’s a dark grey colour about the size of a nickel. It has legs like a crab. It’s legs dont appear to be hairy. So we have decided it must be a crab that hitched a ride on the live rock. Here’s my question is it good or bad? Will it kill my shrimp, snails, or fish? Should I get it out or leave it? I googled but it just confused me. Some say get it out someday leave it. Help. Thanks for the help

[Dary421]

its prob been in there for the last three months or so without you realizing it ,...if its a crab of some sorts id just leave him be,..it'll just be part of your cleanup crew,.it'll survive on eating up any uneaten food or debris.
try and get that picture tho.

[melosu58]

I say let it be. He'll be ok. Almost sounds like a small sally lightfoot.

[Brettdis]

Not a great picture but its definately a crab.

[Brettdis]

Try again