If it's a calcium reactor, it's pretty easy. Your denitrator is going to produce nitrogen as a by-product, so you need to be able to vent this excess gas. This is done by having an opening at the top of the reactor that's connected to about 6 inches of tubing and a shut-off valve.

Since most calcium reactors feed co2 into the topmost point of the reactor, you just remove the bubble counter and add the shutoff valve. That way you can open the valve once too much nitrogen is present and bleed it out. Also, since the reactor already has a recirculating pump, you just want to make sure the recirculating flow is from bottom to top.

Then just replace the araganite material with caribbsea's live sulphur media, or order the sulphur pearl beads from midwest aquatics. The pearl shaped stuff is about 3X as expensive as as the carribsea lsm, but it's less prone to clogging. I've used the carribsea lsm with no problems. Then you can either gravity feed the unit with tank water or use a tom's aqualifter pump to feed the reactor. Make sure you have a good flow control valve on the outlet side, since you want to start off with about 1 drop every 2 seconds for the first few weeks to build up the anerobic bacteria. After the break in period, you can turn it up to a faster drip rate as needed.

If you want to convert a media reactor, it's a bit more of a headache. Here's a link to my tank's thread http://www.maast.org/showthread.php?...s-6-7-11/page7. Look at post #64 for pics and directions. PM me if you need more info.