Hi Revolutionhope,
I have had inconsistent results using the API nitrate test. The problem I have with their test is if you don't shake the bottle sufficiently, not only will the current test results be affected, all future test will be as well since the ratio of components in the bottle are no longer correct. I now use the Sera test. It is more steps, but I like the fact that if I use too much or too little of a reagent and mess up a test, it won't affect future tests.
As for lowering nitrate in your tank, I think the best way is through water changes. I do recommend you add Purigen. My understanding is it won't reduce the nitrate already in your tank but rather it will prevent organics in the water from entering the nitrogen cycle. In other words, these organics won't be creating future nitrates so once you get your nitrate level down it will stay that way.
This is just my opinion of course. Good Luck.