Snails very unhappy

[ScubaSteve]

So for about the past week or so I have been having something weird going on with my snails. First, I was finding my Margarita snails on the sand on their backs. Didn't really surprise me much as I typically find them this way (I am convinced Margarita snails are natures D-students). But then I started finding my trochus snails the same way. I would do as I normally do and hold them near the glass and let them stick on; but whenever I let go they couldn't hold on. Now my cerith are doing the same and so is my strawberry top snail! With the exception of some new trochus I added the other day, everyone is lying on the sand all shut up or unable to hold onto anything! Even the new cerith I added are doing the same.

I am concerned that this is a sign of something big on its way.

To give a little back info:

-I found my velvet nudi sucked into the filter inlet on the weekend, dead. I got him out before he started polluting the tank and am running lots of carbon just in case. Snail issue I noticed after I got him but before he died.

-I recently moved my tank (probably close to two months ago) and just recently had a small diatom bloom (which I attribute to a new substrate)

-I've refrained from cleaning the glass to try and give the snails something to eat until other algae pick up again.

-Parameters are more or less spot on. Not dosing anything.

Anyone have any idea what the heck is going on here?