No, I've never had luck with any algae wafers...as in they don't eat them. The snails end up getting to it first. They seem to really like the HBH Lobster Bites and the Hikari Crab Cuisine.
Nathan uses some sort of seaweed food they like. Perhaps he'll chime in.
I picked them up at That Pet Place, but any decent lfs will have them. The product I purchased is called Julian Sprung's SeaVeggies® Green Seaweed (Porphyra yezoensis). For shrimp feeding getting anything but the 12gr pkg is insane unless you have about 3.2 gazillion shrimp. A small, dare I say, oh say it, miniscule 1/2 sq of one sheet piece fed almost 100 cherries for a day.
Just picked up another food product off aquabid caled snail cookies. What intregued me most about them is the high calcium and iodine content. There is some copper sulfate listed in the ingredients but I have to figure if a snail breeder is feeding these daily to snail that are also copper sensitive how bad can it be for shrimp. I'm experimenting with them in one tank only to see if there are any detrimental effects. I can report that when fed with this concoction the shrimp attacked and devoured the small piece I fed them with gusto.
