IME, dosing carbon sources will work to reduce your nitrates and phosphates. One thing to keep in mind is that this reduction will take a fairly extended period of time. Many of the hobbyists who are using vodka will see less than 1.0 ppm (0.3 ppm) drop in nitrate per day. If you are starting at 50 ppm this could mean 150 days to reduce your nitrates at a controlled level. In the first month, you may only see a drop of 10 ppm, which will not show up very well with your test kit. Plus the low end range of your test kit only goes up to 50 ppm, which means you do not know if your level could be 100 ppm. You should make sure that you use the high end range of your nitrate kit to make sure your value is approx. 50 ppm. Personally, I have a very hard time distinguishing the colors at the range you are at and would not have much confidence in your exact level of nitrates. There is quite a span (50 - 100 ppm) in your high range color chart and very little color change.
