I never measure, I just dump some in. You can't really hurt it, so don't worry about it. I like to put the coral in my bucket (I use a 30 gallon trash can), then start the hose running, and dump in about 3 or 4 cups of bleach. The more bleach you add, the quicker it will work. I leave it overnight, and then start rinsing it the next day. I dump out the bleach water, run another full bucket, dump that, then add dechlorinator and refill the bucket. You can use it within a few minutes if you want, but I like to let it sit another day. Some people also dry it out, but I don't think that's necessary.
Sonny