algae eaters dying 1 by 1.

hi all. i need some help.

i cant figure out what is wrong with my tank.

the CRS inside are fine. so are my BDS and Firereds.

however, 2 Otos and 1 Golden Algae eater(found dead today) have dead mysteriously.

i dont feed them anything cause people say they survive on algae alone.

however, my tank is squeaky clean. no algae at all.

could that be the reason why my algae eaters are all dead?

how can i introduce more food(algae) for them?

all my algae eaters are dead already though.