What is this red plating algae

[panic]

I have a dark red plating algae that is covering the rock in my reef tank. Now it is beginning to plate outwards in half circles. It is business card thick and slightly brittle. It grows only on the live rock. Any ideas what this is and what will make it go away? Unfortunately I cannot get a good pic of it.
Thanks

 

[piercho]

I'm make the assumption that its a calcified algae. Calcified red algae are usually grazed by Diadema urchins, IME. Tuxedo urchins are also good grazers of calcified algae, but are more selective in what they will eat than Diademas, IME. Tuxedos stay small and are less likely to sample coral than a diadema, so its a safer choice. I've had a similar algae in my tank and I'll try to find the genus name of some candidates for you.

 

[panic]

Thanks for the response Piercho. I have a few urchins, but they don't bother it. They tore into the corraline. This red stuff grows outward in addition to encrusting.