Red turf algae, I have the same thing. I enjoy it actually and leave it be. I knocked it out with the turbo snails you suggested but then the rocks looked so bare that I let it grow back out. The tangs graze on it and there's always pods running around in it. It's like coralline but without the Ca/alk uptake that I hate about coralline. Instead, it uptakes nitrates and phosphates... even better.