My OTTB was subject to stone bruises from time to time. In my case the vet had me poultice it with, the name escapes me but it is a minty smelling green gel poultice that contains epsom salt...stateline tack has a similar version called Kaeco Epsom Salt Poultice; I'll have to check my tackbox next time I am at the barn. She says soaking softens the foot and delays a stone bruise from healing..the idea is to harden the foot which this poultice does. I slathered this on the sole, packed it down with gauze and then used ye old duct tape to wrap the hoof and keep everything in place. Be careful using duct tape though...don't wrap the coronet band.
In general, when soaking, like for an abscess, I used warm to mildly hot water to dissolve the epsom salts and also added in betadine; the vet approved the combination and the actions.