Brittle Starfish vs Decorator Crab?

[KrisGeorge]

Just wondering if anyone has experience with these crabs?
I had a Brittle Starfish & an Emerald crab..been in the tank for months. Starfish growing and seemingly very active.
I got a decorator crab & the Emerald crab is killed & I'm pretty sure the new crab is wearing part of the blue shell.
Then I notice the Starfish doesn't come out at feeding any more. It's hiding place seems to be empty & today I see the crab in there.
I didn't read that they were predators but I don't know what else could have caused both of these two animals to disappear
Water tests fine except for high Phosphate, which I'm trying to combat.
So, it's it the crab or the Phosphate?

 

[Sleeping Giant]

Good question, I'm interested in the answers too

 

[Uncle99]

No crab can be trusted.
The will eat, anything they can catch.
As long as your OK with that, no problem.
With over 4,000 variations, hard to accurately identify, and easy to go rogue.
Remove the crab.

 

[KrisGeorge]

Well the star fish is gone now, so probably don't need to remove the crab. The other fish are never bothered by it..