I had large river stone they couldn't swallow when I had my tank. The turtle love to move the rocks around and redecorate. I would dump in a bunch of snails from my others tanks now and again and they would spend hours searching through the rocks for snails, so gave them a treat to eat and to hunt for and kept them active.
20g platy, , 2 x 10g shrimp, 3 x 20g shrimp, 7.5g shrimp and 1 great dane/mastiff puppy.
Sump Pimp #2
My Tanks and my shrimps