weird brown things covering live rock??

[mxpro32]

there are these strange flat brown things growing on my live rock in my 28 gallon. they are about an inch and a half across and are overlapping each other taking over a big piece of live rock. and now i noticed one growing on another rock in a different part of the tank. they are pretty ugly and i dont want them to keep growing does anyone know what it might be?

[Toyfreek]

sounds like a macro algae, possibly sargassum. Without a pic it's like guessing when it will rain without a radar....who knows?

Toy