Not free swimming... Slug-like/leech like... appear white in color in the cleaning tube but dark brown to black in the bottom of my 5 gal bucket...
Please help
also.. not attached to any fish. they appear to be in the gravel
Planaria. Harmless guys. Try not to overfeed though because food leftovers are their source to start producing too much. Since these guys produce as well by severing them apart, better not do it. Vacuum them off and limit food rations for the next few days. You'll find significant difference in time.