Was the rock fully cured? You may have also restarted the cycling process, the brown algae is usually due to poor water quality or the tank just being newly cycled, thats what mine did at the end of its cycling process.
When I grow up I wanna be a marine biologist
100g fw fluval 404, 403, mag 350 w/biowheel30
2 Tiger Oscars, 6 tinfoil barbs, 2 silver dollars, 2 clown loaches, 1 red finned pacu, and 2 bal sharks
55g salt water with 2 clarki clowns, 3 damsels, and a diamond goby, 60# lr
, 40# ls
, 3 bulb anenomes