I soak my stones 24/7 in a closed, opaque container. No light, there shouldn't be anything growing in it (but I still change the water when it starts to seem cloudy or whenever I feel like it, but the city water here has chlorine in it anyway).
Soaking, they all seem "softer" to me and like they're working just a little better. YMMV, though, as I like a "soft" stone. . .I've noticed when I'm done on a particular stone, the instead of the stone feels like it stops "grabbing".
Either way, good buy. I love those three stones. . .a mirror polish with minimal work. Great for a lazy dude like me. :-D
The Barefoot Woodworker.
Fueled by leather, chrome, and thunder.