[Delphinus]

No need to try to lower it, that will happen anyways as the reef starts to draw stuff out of the water. Coraline algae, any stoney corals, clams, snails, etc., all take calcium out of the water, and they need alkalinity to be able to do that. So generally say you start off with Calcium at 400ppm and alkalinity at 4.0 meq/l. As things start to grow, they will pull both the calcium and the alkalinity downwards. Once the alkalinity gets lower than NSW, things will not be able to pull calcium out of the water anymore (or not as easily as before), and the calcium will tend to come back up (assuming there is a source for this calcium). So the long term strategy is to keep both levels nice and high, and that's where things like buffers, two part additives, kalkwasser topup, or more complicated gizmos like kalk stirrers/reactors, calcium reactors tend to get used. This of course is a great oversimplification of things but as a model it kind of shows the relationship between the two values and it works for me. A high alkalinity tends to pull the Ca down; a high Ca level tends to pull the Alk down. A see-saw effect.

Tracking Ca and Alk in tanks with minimal Ca draw, such as fish-only tanks, or tanks primarily filled with softies, is probably less urgent than those tanks with high Ca draw such as those with SPS, or even LPS, clams, and so on. But even in the case where it's less important it's still nice to see things like coraline algae grow and so on. So even then it's still nice to know your Alk and Ca values are within good ranges.

cheers