Proper Magnesium levels, Alk and Calcium will do wonders for stability and coralline. Many salt mixes do contain magnesium; however they usually don’t contain enough to keep levels ideal with your basic water changes. Actually, in some cases I have actually lowered my magnesium levels by giving to many water changes. Some salt mixes are better then others, but I would never rely on water changes to keep mag levels in the ideal range (I like 1350 or higher). When I first started I had terrible coralline growth. However It was a different problem that got me to check magnesium levels, once all 3 were in their proper range Mag, Alk and Calcium I noticed that coralline grows even under duel 250s. There are other clues to low mag levels, but this should be a good starting point without confusing the issue. Good Luck.