Hi, I have a leftover calcium reactor from years ago when I had a large reef tank. It is an MRC, older, but similar to the CR-4 model. It will need nylon thumbs screws on one side, a pump, and other stuff to hook it up. I never used it, but it came from a reefer that had been using it. In Ofallon, Mo. FREE - I can't think of anything to do with it.