Here's my thought on the whole water change concept:
First, for those who say you do water changes to remove excess nitrates, if that were true we would all have very high nitrate levels. In fact our tanks would stabalize at a point where the weekly addition of nitrates (i.e. food) is equal to the weekly removal. So if we did a 10% weekly water change, then we would only be removing 10% of the nitrates weekly. Or one could say we are leaving 90% of the nitrates behind. Based on that, water changes for nitrate removal is a complete waste of time. Water changes, like skimmers only deal with a percentage of the waste levels, and that percentage is NEVER 100%.
What does that mean?
There are 2 things we need to do to a system.
First, we need to remove all excess proteins that we add in the form of food, that fish convert to waste (minus the amount that becomes livestock biomass). We do this with quality protein skimmers, media reactors, algae turf scrubbers and macro algae. Things like skimmers and reactors can take out large percentages of waste, while algaes can remove it to 0 levels. the heavier stacked your system is, the better your waste removal systems need to be. Water changes will only take care of a small percentage of the waste problem, and relying solely on that will set you up for nitrate problems.
Second, we need to replenish the other things in the water. The most obvious is carbonates and calciums that are used up by all the corals and other invertabrates in the tank. There is also magnesium that is very important. But it doesn't end there as many other minerals are needed in a healthy aquarium. Water changes DO replace those last chemicals. But if your tank is heavily stocked, you may need to augment water changes to keep easily measured levels like Alk, Calc and Mag at preferred levels. And, if you want to limit water changes, as a few of our top notch posters and aquarists do, dosing is a very effective means of maintaining a stable system.
So with a quality nutrient removal system of skimmers, resins, reactors and algae, coupled with a measured and monitored dosing regiment, you certainly can maintain a stable aquarium with very little in the way of water changes. Is it cheaper than simply doing water changes, I don't know. But dosing pumps are not cheap.