I'd soak that rock for a couple days since it's porous and I wouldn't do the DW. If you only had a small amount of BBA you could have easily done a spot treatment with hydrogen peroxide in the tank. Plus if you don't correct the problem that caused it to start growing then it will come back.
How long do you leave your lights on? What kind of lighting and bulbs do you have? What is your WC
schedule and how much do you change out weekly? Is the tank planted? What is your nitrate reading?