Which star Decimating cleanup crew?

[bs21]

ok well as the title says I hae two fairly large stars for my tank at least. One of which is what I believe is a serpent star (brown mostly, larger body and black bands and small spines off of legs). The second star is what I believe to be a brittle star (Deep Black, tons of spines all over, little white stripes at points, smaller body compared to length of legs). Well as the story goes I have these two stars and one of them ate two pepermint shrimp and pretty much the majority of my hermits/snails. maybe the hermits killed the snails for shells but where did the hermits go? anyway the reason i suspect one of them is the black brittle started as a very small hitch hiker on a coral rock with a ton of baby stars sticking out of it also. Well this brittle has become ginourmous in a couple months. Every time I feed the tank it comes flying out of the rocks to grab all the leftover food it can and even grabbed one of the shrimp as it ran by. The shrimp escaped only to disappear a couple days later. Now the other star pretty much hangs out in the back of the tank and I usually don't see much of it, which makes me feel less likely hes the culprit but then again he may just seem innocent bu really is a voracious killer of my tanks smaller inhabitants. So if any of the starfish experts can weigh in here on which is the most likely culprit so I can bring some peace to my reef by finding these guys a more suitable home.
p.s. Tank is 30 gallons which may not be suitable for food source maybe which is causing them to search out alternative food sources. I did not buy the stars but they are there and not easy to remove without removing rock. But so far alive and healthy. Will be moving to a larger tank soon if I decide they can stay lol

 

[natclanwy]

Serpents and brittle stars are generally safe with your cleanup crew but they are opportunistic feeders and could have gotten a taste for hermits and snails although I'm not sure how they would remove them from there shells. Shrimp on the other hand can easily be consumed.

 

[ophiura]

I personally would not rule out another predator like a mantis.
Or acclimation issues -
How long did you have the hermits, shrimp?
What are your parameters?
Hermits are actually voracious killers of each other if you are not careful.
Basically though it is possible you have an aggressive brittlestar - it seems unlikely with how much maybe you've lost. They do need to be spot fed. But I have 10 large brittlestars in a 45g - the number in your tank is not a problem. So in general I am not convinced either of the stars is really the culprit without knowing much more about the situation in the tank.