Doing super frequent water changes.. what can go wrong?

[Delphinus]

We might be getting into two separate topics though here: reefbuilding and nutrient management. Dosing is really more about managing parameters that are directly responsible for coral growth; nutrient export helps growth in that nutrient buildup will inhibit growth so removing nutrients (and by extension, ULNS) will remove those inhibiting factors. But even a zero nutrient system won't grow corals if there is no calcium or alkalinity or magnesium to begin with.

So. Water changes does benefit both goals by removing the baddies and replacing the goodies that get used up. Certainly there are tanks out there that use only water changes as the primary tool and these are nice setups. And indeed, do enough water changes and you might not really need a skimmer.

But what I think you'll find is that with water changes alone, you will only be able to go so far with it. In a low demand system, it may be enough forever. But in a high demand system (such as one with SPS), the draw on the calcium and alkalinity is not linear over time. Ie., as your corals grow bigger, so too does their apetites for calcium, and thus you have to add more Ca and Alk to compensate. At a point you will find, I think anyhow, that water changes alone won't cut it, and you have to manually replace Ca and Alk anyhow (either by dosing or by calcium reactor). The main thing about this is that the Ca and Alk is now decoupled from the nutrient export - which ultimately is a good thing because the rate of Ca and Alk usage likely isn't directly proportional to the nutrient buildup (which is going to depend on the fish load, and how much/how often you feed, etc.)

So, I'm not saying I think it's a "bad" idea, but I think it's just not the most efficient or cost-effective method out there.