Hello; You have been given some good advice. Let me add to it. First suggestion is to do the water change (WC) more often. How often is to be determined by results. It may be once a week, twice a week or even every day. When you get it below 20 ppm will be a target most find acceptable.
I get the idea of reduced feedings. Somethings to keep in mind. Even a fish which is not fed at all will continue while alive to metabolize using muscle tissue and eventually internal organs after it uses up the fat reserves. So there is a limit to the effectiveness of reduced feedings. There is also the question of he smaller bits of flesh cast lose when the fish eats. Some fish are very messy eaters. May be that the fish you fed to your fish should be cut into smaller bits that it can swallow more whole. In two weeks the uneaten food will make it way into some place in the tank. If not the filter then in the substrate or other places such as décor. Maybe a good general tank cleaning??
last thing is are the test results accurate. Nitrate test needs to be well shaken. A lot of shaking needed. Also the vials need to be clean. I suggest using distilled water (or DI water) to clean with. Rinse for sure and even allow to sit filled with distilled for a few hours. The distilled water should removed many contaminants. Those contaminants might be skewing your results.
