sump pump has a screen on it and it was verry dirty
mine was only a month oldI clean mine every couple months... if that helps any
Hi Fizban
WELCOME to Reef Sanctuary
It's very normal for a tank that has been running for less than 6 months to go through a series of algae & diatom outbreaks.
Your snails could have died from ammonia & nitrites during your tank's nitrogen cycle. And crabs love to eat snails whether they are dead or alive . Sorry for your beginning difficulties.
It might help us to help you better if you post your test results in number values.
Are you testing your water with your own test kit or taking it to the LFS (fish store to be tested
Hang in there...getting started and getting past the UTS (ugly tank syndrome) takes lots and lots of patience.