Look, if you have at least 1ppm of NO3, then you have enough nitrogen in the system, beyond that, it's just the ratio compared to PO4 that matters, not the actual number itself. But I agree that mixing sps and mushrooms is kind of hard, but not impossible, in fact, some can take high light (yuma being one of them). As I mentioned before, some corals may not like a particular system, but do just fine in another, it's all trail and error.