I use a sulphur denitrator. My nitrates were always high and couldn't lower them even with a DSB. Within two weeks of setting up the denitrator my levels went to zero. that was 4 months ago. Take soem time and learn how to tune it. Once the levels hit zero you'll see the sulphur starting to clog. When that happens remove about 50% of the sulphur, and it will be fine for a month or two. When it starts to clog remove another 50% leaving 25% of the original total and that should do you. The reason fro the large amount of sulphur to begin with is to remove the large amount of nitrate quickly. Once the levels are down, you don't need that much to maintain it. Good luck