The way you have your tank set up is the culpruit of your nitrates. I suggest that you not have angelfish or tangs in this tank as nitrates tend to cause HLLE.
What about LR?
To lower or get rid of nitrate, you will have to redesign your setup. LR, LS, refugium, etc. Mechanical filters such as canisters, wet-drys, etc., do not complete the export process of nutrients in your tank. They do excellent with ammonia, nitrites but stop there. A more natural type of setup will eliminate this problem.
For instance, I have no mechanical filters in my tank. It never cycled and I have had zero readings from day one.
Do a Serach here on HIGH Nitrates, Nitrate problem, etc., so you can get various input. But I can tell you with certainty that your problem is your setup. If you added a few more inches of LS and added LR, you would likely resolve most of the problem. As I said, do a search here for more input on nitrates.