Dead Shrimp ?!

So I just got a peppermint shrimp and the little guy was happy for about 3 days, then this morning I seen him and everything was good.. But when I got home later on today he was dead. And a bristle worm was going to town on the dead shrimp.



I tested my levels in the water and I got everything at 0 except ph which was at 7.8, what do you think caused the death ? :bawling: