They have been around for many years... but are coming back into vogue now. I own one, the H&S model and it took my nitrates in my 90G from around 50 to under 5. There is no food needed... basically its just a media reactor with a small pump on it, like the carbon or GFO reactors. You fill it with sulphur media (bb sized is best as it doesn't clump) and then run it wide open for week or so. Once the bacteria has seeded in the chamber, you start reducing the drops until the effluent reads 0 nitrates, then you maintain that drip rate. Mine is about a drop a second or so...... It takes a good 3 weeks to start working and probably another 2 or 3 to get nitrates down.
Some things to keep in mind... when you first start and are running it wide open, watch your pH because it could dip slightly. Mine hasn't but its been reported. If you fill the chamber you leave the top 1/4 empty and 1/2 of sulphur, the other half throw in some calcium reactor media, I use the big coral chunks Gen-X product at the top... this buffers the water going through and should take care of any pH issues.
If you have a chronic nitrate problem, or don't want to run a fuge, its a good investment. Marc built one with an RO/DI unit but I don't know how much success he is having currently. I would wager that any media reactor could be used as one, such an old calcium reactor or any of the reactors made for carbon/GFO. I would avoid the two little fishies reactor though because of the pressure involved, they are not the most sturdy things around.
