Yes, I am feeding bbs (and moina in addition to grindal worms) to my aggies. I see hydra catching not only bbs but moina as well. In my orange flash cac tank I saw adult daphnia being eaten by these little nasties. Since my moina and daphnia tanks are free of hydra so far (thank goodness), I suppose the hydra are making rounds of my tanks. I bet some of the hydra are injured but not completely killed by fluke tabs or their eggs are not harmed by fluke tabs.