1/3 stock salt, 1/3 trace mineral, 1/3 dical phosphate. All can be found in 40-50 pound bags at co op. I also add grape kool aid that's premixed with sugar in the tub with it.
The grape kool aid works miracles for getting them started in your site, get the wally-world great value stuff with sugar added, no need to add it again once it's established.