i wrote this in the black powder thread:
If you have at least 3-4wpg (ok, anti-WPG people, gimme some slack on this one) all you need to do is keep Ca b/w 420-450 AND dkh b/w 9-11 at 8.2pH and you will get coraline growing out of your ears ... it is IMPORTANT to keep both ca and dkh up and BALANCED at these levels
I also found it useful to keep salinity up around 35ppt. You will need a refractometer for an accurate readging.
coraline is nice and it covers up some ugliness to the rock, but it becomes a pain later. once you see pink spots you also know that your tank chemistry is in-line and your corals should thrive (assuming the bad nutrients are being kept in check)
coraline is a calcifying algae. phosphate inhibits calcification. so if you are doing everything right and still no coraline, look at po4. It needs to be below .25ppm for best results. i belive natural sea water has po4 levels of around .07... a lot of young tanks have po4 higher than 2.0... thats nearly 30x the amount of po4 in natural reef water!!!