I usually go with 1 cup of bleach to a gallon of water (different people have different quantities, I like to kill everything for sure so I go strong), you only have to do the bleach once, the water changes would be with the water you are soaking it in, to help get the tannins out. This also helps waterlog the wood a little so it doesn't try to escape through your glass top when you fill the tank. There are two good ways to get rid of the bleach, one is allow it time to dissipate which the water changes wil help with, the other is dechlorinator which of course gets rid of it as well. Just make sure you use straight up chlorine bleach, nothing with scents or additives.