Hi ya, love the salt,
Two things usually prevent the growth of coralline algae in a reef tank:
1) The absence of coralline alga spores
2) Competition from faster-growing non-coralline algae
So, you must first provide a source for coralline alga spores and induce spore production by keeping the alga happy. They have all the requirements of other algae, but can get by on less.
That's why you find them thriving even in nutrient-poor, light-poor, herbivore-heavy locations (cave underhangs, etc). This does not mean that they prefer low light and low nutrients, only that the poverty of light and nutrients keeps out competing algae.
[Flip over bare-looking reef rubble in nature, and you'll find the pinks and reds on the UNDERSIDE of the rubble. Why? Because they don't have competition (and also they are protected from the harsher herbivores like certain sea urchins. The topside of the rubble gets enough light to allow greens and browns to flourish, choking out any coralline algae: the colonizing greens and browns also invite the attention of herbivores and if these happen to include the severe urchins like Genus
Diadema,
Echinothrix, etc., the rock is constantly grazed bare! Ooops, I'm straying from the issue... ]
So....here's what you do:
Get as much of that competing algae out, by hand if you need to. Reduce nutrient input, or invest in more detritivores to clean up the scraps before unwanted algae can utilize the rot. Boosting calcium binds down usable phosphate and other nutrients, and provides corallines with building material.
Boost your herbivore complement. I've heard that
Tripneustes gratilla is an urchin that isn't as harsh a hebivore as some others --yank it out if it's too severe.
Trochus snails are proven winners. Fishes like tangs are IMO useless by themselves: they just graze enough to ensure future regrowth (self serving, eh?) --they do reduce the length of growths to where the snails can get 'em.
AFTER all that, ensure a source of coralline algae spores. If you have to buy a really-encrusted fist-sized rock, do it. Place it in a partially shaded zone, and encourage very good flow through the location to disperse spores.
HTH
horge
PS: Bill's right about ESV B-Ionic. Used properly, it can indeed boost coralline
algae growth, but go easy on it if it starts to encourage even the mildest dinoflagellate or cyanobacteria outbreaks (red/tan slime or dark blue-green film): that's a sure sign you're overdosing --and the manufacturer's recommendations on dosing seem a bit on the heavy side
