Just about had it now!!!

[Reefer Rob]

I'm going to out on a limb here and say I think it's your sand. In my 180G that's been running since January I've gone to 1" of sand for aesthetics that I gravel vac once a month or so. Looking back, the only thing sand has ever done in my tanks is increase nitrates. The more sand I had, the more nitrates I had.

In my last tank I run an remote DSB and had 20 ppm nitrates. After I took it off-line they went to 10 ppm within a week.

With 2"s of sand you would be safe to suck out 1" and gravel vac the rest. Guaranteed you're going to get a ton of crud out of there