Forgot to mention ...
I've had longspine urchins for years now, and the only problem I ever had was when one got big and started eating tiny SPS frags. I solved that issue by feeding it nori and shrimps whenever it would climb the front glass.
It became a routine. He climbs and I feed.
I returned the large longspine when he outgrew the tank and bought the smallest one I've ever seen in my life. Was about half the size of a ping-pong ball. Seriously was super tiny. I never saw it for months while it grew.
Then I finally see it out roaming around and think, good, now it'll start to eat some algae.
Well, months go by and it grows. I try to hand feed it as I did with the first one, but this guy will have no part of feeding tools. So I figured, meh, and let time go by.
Forward a bunch of months and my flaming sun zoas start to disappear, then my watermelons.
I looked for nights on end for predators ...
Move forward a week and I catch the longspine on the watermelons before lights on.
I thought maybe it's just cleaning the newly exposed LR.
Then a few days later I see my lemon drop zoas are gone, and the urchin is sitting on top of my la lakers.
I push him off and see I've only got 3 polyps left
Son Of A Coral Eating Couldn't You Have Continued Eating The Watermelons ?
So, after a short time of thinking about putting the longspine in the garburator I returned it to J&L, along with the 2 pincushion ones that were killing my snails by up-rooting them from the sand and carrying them around for days without food.
I've gone back to Strawberry tophat snails
I couldn't do this back when I bought the urchins as I killed off a lot of snails by dosing too much peroxide to kill the hair algae.
Live and learn
So many things to NOT do in this hobby