It is the Sulfur Denitrifier XL by Midwest Aquatic. They send the sulfur mixed in with freeze dried bacteria. The freeze dried bacteria is supposed to jump start the system so you don't have to wait 4-6 weeks for the denitrifier to grow the bacteria. Midwest Aquatic thought it should be about 21 days to get a -0- reading at the outlet. I don't know why mine "matured" so quickly. Maybe my stupidly high Nitrate reading accelerated the process? The sulfur is the food, you don't have to feed it anything else. If I understand it correctly, the water passes through the sulfur where nitrate is broken down by the bacteria which breaks down the nitrate for it's oxygen. The water becomes acidic then passes through the Calcium Carbonate to be buffered before returning to the tank?
My nitrate tank reading is over 200. It pegs a quick drip stip and my drop style test kit is as red as you can get immediately even though it is supposed to be given 10 minutes to develop. Last night I tested 2.5ml tank water with 2.5 ml R/O water with my drop test kit (max 100 reading) thinking I could multiply my reading by 2 to get the actual but it was off the chart.
I had been fighting a nitrate reading, that I thought was 20, for about 6 months. BTA, snails, leather, etc had all seemed to be sliding downhill plus I was really having a lot of algae. I increased flow, removed undergravel filter, removed fluval pads, added de-nitrate, added nitrate sponge, added skimmer, cut feedings, removed fluval bio media, added more rock, tried AZ-NO3 etc. No change at all in 20 nitrate reading, but tank continued to not seem right and get worse. My zoos started to deform which led me to find that can happen in an extremely high nitrate tank.
Finally:
I decided to double check my readings with a quick dip. Turns out my Nitrate test wasn't working and Nitrate was acutally over 200.
My knee jerk reaction was to attempt a massive water change, but decided instead that they have probably been high and rising for 6 months so I wanted to take the time to find a permanent solution (other than daily massive water changes and the 50 other things I tried).
I'm estimating that I'm getting 10-12 gal a day of nitrate free water into the tank through the sulfur denitrifier.
I suspect that I'll be able to get about 15-20 gallons a day of nitrate free water out of the outlet as it matures. This should allow my nitrates in a 120 gal tank to drop pretty quickly and stay near zero.