Longspine urchin and 3 peppermint shrimp died, rest of livestock "good"

[firstsalttank91011]

Hello Reefing Community,

We have a 10 week old tank that have slowly been adding livestock to. Check all parameters prior to any additions as well as took a few weeks to get salinity (~1021) to match local fish store as ours was higher (~1025) than theirs initially.

Recently (10/2/2021, picture below when bought) purchased a longspine urchin that died 12 days later (picture below under 10/14/2021). In that same week (10/6 - 10/14) 2 known peppermint shrimp died that we directly know of; not a molt as we saw one die in front of us and saw both devoured by our Nassarius snails and hermit crabs. Only the smallest of the peppermint shrimp is still alive. We also have our LFS check all of our parameters prior to discussing any additions and they confirm all looks good and only add based on their recommendations.

Wondering if anyone has any thoughts as to what could be happening and anything additional we should be checking for.

Additional Notes
Ph 8.2 - 8.6
Ammonia, Nitrate and Nitrite - 0
Temperature 77 - 78.5
1.5 hour acclimation process
Salinity 1021
Alkalinity (dKH) 8.4 - 9.52
5 fish (all small) 2 Clown (8/10), 2 PJ Cardinal (9/17), 1 Sifter Goby (9/25)
1 Scarlet Skunk Cleaner Shrimp (9/25)
1 Fire Shrimp (10/2), 1 Longspine sea urchin (10/2 - 10/14)
4 Peppermint shrimp (1 - 9/17, 3 - 9/25)
Lots of snails and hermit crabs slowly added (8/27 - 10/2)

10/2/2021

10/14/2021

Thank you all as always for you insight and guidance.

 

[blaxsun]

I find urchins can be hit and miss. They're either healthy or already on a downward slope when you get them, and this usually takes a few weeks to play out (even if acclimated properly). I had 1/3 blue tuxedo and 1/2 green urchin survive the last transition.