Yeah, I have two blocks... Thank you C4. Set them and leave them there... In a low flow environment for denitrification. If you don't have a low flow area, I'd make one... Else you're just using it for nitrification and at that point, I wouldn't bother. Most reef tanks have no issues with nitrification and you might even add to your nitrate issue if its too proficient at nitrification.
Jestep is correct, don't rinse it or you'll reset your bacterial population. Just a note, on some of the bigger forums, I've been in discussion with others on the potential leeching of Al into the water column from those blocks. I haven't had any issues yet but my Al levels are definitely elevated.