What kind are they? Do they have a conical shell or a rounded one?
Adding a snail eater (loaches, assassin snail, etc.) can help clean them up. You can also put cucumber pieces in and remove as they get covered in snails. Personally I like to keep them in the tank - they are unmatched for tank cleaners.
As for the black bear algae, I’ve had success using scuds (freshwater amphipods) to destroy it. I had to remove decor to put with them for best results. Given the size of the ray and aro, they may not pay any attention to them directly in the tank.
At this point I’ve just learned to live with the BBA - I’ve grown to like it.