Ha, cranberry, I have almot he exact same set up. i have a lionfish amongst a bunch of white rocks in a 90 gallon. my brown algae went away in about 1.5 weeks. no biggie.
unlike you though, I got the lion with the tank and I want a reef so im looking to get to lion to a new home so I cna move forward with mine. hes about 9-10" and floats around like a ghost. he stares and my 2 year old like a light snack when he gets close to the tank LOL