I have 2 mystery snails i added to my 55g. See sig for stocking. i was wondering if i could add 2 more? Right now I'm using them to devour my diatoms. When i have control on the diatoms i will supplement with pellets and veggies.
I also have a 55 and just got my 3rd today, just make sure to put some veggies in there and algae wafers. I don't know why the bosemanii rainbow always eats the cucumber instead though. Mine are mating like crazy, just watch for the eggs at the above the water line and get rid of them if you don't want a lot of babies.
Apple snails usually are not very proficient at eating algae. Is the lab pestering them at all? As far as your stocking, you could add more. I do think you should be supplementing their diet with a calcium rich food though.