The purpose of water change is more then just reducing nutrient, it also replace the element and other stuff used up by the coral. Unless u are dosing element into the water every now and then, the element will be used up. For Lps tank, the observation is not so obvious but for sps tank it is quite obvious.
Guys good to read more and not just follow reefer advice. Every reefer tank is different so what he/she do might not be suitable to your tank. One of the example is a reefer tell me he is told by another reefer, only need to change water every 6mth and the tank is doing well but why his tank is not doing well. The reefer that told him this method is keeping softies and Lps tank, while this newbie here is trying to go for full sps.