Reborn is the calcium reactor media I use for my 400g reef. It's clean, nice and coarse and is ready to use right out of the bag.
This is a 4 kilogram bag (8.8 lbs) of media, which is a little more than most medium-sized calcium reactors could hold... so you'll have extra to top off with later. Buying in bulk saves money.
Reborn is a product of Two Little Fishies.