I have very dry skin, and I also have a fishroom so I spend probably a lot more time than most with my hands in the water. I had just been skipping the lotion but this winter was really rough on my skin so eventually that was no longer an option. I started using organic coconut oil in place of lotion and, although I do wait until it soaks in to put my hands in the tanks, I no longer feel the need to "scrub up" beforehand. The only ingredient is organic coconut oil so I figure that's about as fish-safe as it's going to get. Even with a primarily natural lotion like Burt's Bees, I could scrub with dish soap and still smell the fragrance on my hands... that can't be good.
A big tub of coconut oil costs about 10 bucks. Maybe it would be worth looking into, at least for the days that you know you are going to have your hands in your tank.