A Coralline How-to and Why

Coralline: what good is it, what harm is it, and do I want it? Informational.
Coralline is the purple-violet stuff on your rocks.
The bennies of having it on all your rock: a good coralline coating principally means other, more objectionable algae can't grow there efficiently. It probably (my guess) does limit efficiency of water reaching inside your rock, but if you have holey rock, you have plenty of exposure, including the part sitting on the sand, where this stuff won't grow.

The purple color is rather prettier than basic brown, which is the way all rock tends to look after a while in a tank.

The immediate downside is (especially for acrylic tanks!) its tendency to grow on the glass/sides/downflow, equipment, and anything else that sits still long enough. There's no easy way to get the pink freckles off acrylic: best I've found is FREQUENT cleaning with an appropriate scrubber, and if it does get on, early application of the edge of a credit card. The stuff can really take a tank, so if I had an acrylic tank I'd be REAL careful about my magnesium levels.

Yes, magnesium. If you have mg around 1200-1300, as is recommended for stony coral reefs and clam tanks, you will also have coralline algae spreading. And here's the catch: without enough mg, you can't keep your calcium levels steady; but WITH enough mg, you may have coralline growing where you don't want it.

Ecologically, corallines provide microhabitat for reef organisms, they help 'glue' a reef together, and they are food for many species. I always sigh when I hear some reefer railing against some little invert 'eating his coralline'...and threatening to nuke the species---as I sit there cursing the pink dots I try to keep off my glass. Consider it a renewable resource, nicer than hair algae, but about as stubborn.

If you want it, imitate my tank parameters, from my sig line, and if you have a little 'seed' of it in your tank, with adequate lighting, you'll see it grow.

If your coralline should turn white, it's called bleaching, and it can result from tank temperature spiking over 80 in the presence of bright light. If you ever get into that situation, cut the lights off and check your temperature, crosscheck the accuracy of your thermometers, and also run a water chemistry check.

It doesn't grow fast, but if you keep your alkalinity, calcium, and magnesium at the levels in my sig line, it will grow. Just don't expect it to run wild on rock: it seems to 'prefer' tank glass, in the cosmic injustice realm of things.

You don't absolutely need it, but it's nice if you can get it to grow where you want.

If you are faced with cleaning up an old corallined mess of a tank, the basis of the coralline is calcium carbonate, which does respond to white vinegar.

In general, just maintain good parameters and have one tiny sample of coralline rock and you're good. Most advanced aquarists in your reef club can help you out with that!

And if you haven't made contact with your local reef club, we have club listings on RC. Look yours up. They're a great resource.