Reading the rest of the post, I’m going to lean towards those dying inverts not finding the adequate food source. Based on the shrimp doing fine, as well as the anemone which are more delicate inverts, crabs & snails which are much hardier, might not be finding a good algae source. That’s my assumption without looking at your tank or having a positive ID on the type of algae growing in your system. Agree with Mojo, a full picture of your tank would help tons.But the thing is my large Clark clown HATES and WILL KILL any shrimp and also most of my Inverts end up dying but I’m keeping fish and coral completely fine and even an anemone (which are known to be hard to keep) alive and doing really well