I just found this info on the web. We actually switched food for our Hermits to Flukers brand. They seem to like it better. When we aren't feeling lazy, we do give them bits of fruit & veggies, but it looks like Hermits can tolerate a bit more protein than Moon Crabs. Can you try making mini salads? Best of luck! *** *** *** *** *** *** *** *** *** *** *** *** *** *** "In captivity, Halloween Moon Crabs enjoy a varied diet and will readily eat just about anything they are offered including some bits of organic matter. Important: Despite your crab’s food desires, you should avoid giving protein-rich foods (such as cricket, bloodworms, live brine shrimp, etc.) all the time. It should be given only as a treat or in addition to other food for extra nutrients. Personally, I would say that their diet should be: at least 90% herbivore (fruits, berries, flowers, leaves, plants, vegetables, etc.) less than 10% protein. Be very careful with that. For example, under high humidity, protein food gets moist and soggy very fast. As a result, it will mold and mold kills crabs!"

Yes, they will sink.  I don’t know if they are good for other types of crabs as I only have experience with hermit crabs.

I have never put them in water, I put them in the crab's food dish, which is dry. He loves them!