Reducing Nitrates

I haven't performed a water change for about a week and a half and nitrates are still around 2.5 ppm as measured with a Salifert test kit. It's hard to see in the picture below but the sample color is closest to the 2 ppm color.

From Paul's Reef

One thing that is really nice about the Salifert nitrate test is that once your sample is <= 10 ppm you can use the kit in low range mode. To do this you simply match the color my looking through the side of the vile and then simply divide the number of the closest color by 10. In the example below the closest color is 25. So my nitrate level is 2.5 ppm.

From Paul's Reef

Getting my nitrate to this level has taken a long time. I'm still not sure what finally worked. Was it the deep sand bed, the Chaeto algae, the algae growing naturally in my refugium or the new light bulbs? The most recent change was the lighting. After I replaced my bulbs is when I saw the nitrate level drop below 10 ppm.

One other variable I forgot to mention is that I ran out of Kent Marine Tech-I that I was using to supplement Iodine. I ran out about a two weeks ago, about the same time I replaced my bulbs. I originally started supplementing because my Xenia were not looking good. Right now they are pulsing faster than I have ever seen and rapidly dividing on their own. I will not add iodine again unless I see things degrading again.