Dead Turbo Grazers

I bought about 10 Mexican Turbo Grazers a few weeks ago to help take care of
a hair algae problem in my 30-gallon tank. Nine have died within about 2
weeks leaving me with only one. My water parameters are testing well NO2 =
0; NO3=0; PO4=0; Ca=440; pH=8.3; S.G.=1.024. I have about 10 hermit crabs:
red legged, blue legged and the ones with black&white legs. Do you think
that there's something in the water quality or could the hermits be eating
them? I'm running on a wet/dry with bioballs, an urchin protein skimmer and
two powerheads in the tank for circulation.

Thanks!

Maddie