How do I lower my nitrates

The light for the 10 gal was a 36W Actinic Blue-Pink PC that I had built into the original light strip just like yours. It cost about $40 for the parts and $20 for the PC tube.
The light for the 9 gal was the one that came with it. A 2x18W PC tube fixture, again with Blue-Pink tubes. These Blue-Pink tubes make colors pop, just like a combination of two T5 tubes, one Actinic Blue and one pink/Fiji Purple.

Since the coral look good, I wouldn't worry any more about N pollution. I rarely test for pollution because the coral are the best indicators of problems.