dead decorator urchin what issues can it cause

[PeterEde]

So I have been having issues with NO3/PO4 being higher than normal lately.
I realised I've not seen my decorator urchin in a few days.
I just found it's empty shell 2 days ago.

Would that have been the cause of my issues?
I did test for Ammonia a few days ago which showed no Ammonia but by then it could have broken down to NO3 and other toxins?

 

[Spare time]

It's really difficult to say imo. Unless there is something obviously wrong with the tank water, I don't think you will find an answer

 

[PeterEde]

what killed it too?
I'm pretty sure there is at least 1 maybe 2 pistol shrimp. It was in the tank from just a few weeks old. Tiny little thing and survived 12 months. I have a long spine urchin that's been with me since week 2 and it's very healthy.
Curios to know what killed it but will never know