on a somewhat related note, any ideas as to why corraline grows easily and readily on anything aritificial I introduce into the tank (powerheads, plumbing, cleaning magnet, etc..) but I cant get but a couple of spots to grow on my glass where I really want it?
Same here, I have it everywhere but just spots on the back glass. Since I've been keeping up the alk & ca, it does seem to be spreading better. Which brings me to question, how much corline is necessary, & exactly what is it doing to help your tank?
One of the reasons for rapid coralline algae growth on newly introduced objects is that the conditions are right at the moment you introduce the new piece. Things that have been in the tank for a while will have other micro algae/bacteria covering their surfaces. Some are very hard to see with the naked eye. They were there when conditions were favorable for them in the tank. Coralline algae will have a harder time colonizing there because it will have to kill the existing algae or bacteria first. A new object doesn't have anything on it and is new real estate. This is especially true on well established tanks with low algae amounts and high calcium/alkalinity levels (as the conditions favor coralline rather than other macro/micro algae).
As to how much coralline is necessary that is purely a personal issue it has no bearing on whether or not a tank is healthy except as an indicator of calcium/alkalinity levels. It is actually robbing calcium/alkalinity from your stoney corals so in that sense it's a bad thing.