First, what size tank is this? SAE's get big, quickly, especially in a high algae environment. They also enjoy being in groups, so 3 at the minimum. I would put 3 in anything less than a 55g.
That being said:
I have removed BBA by using the following technique(s). I performed them in this order:
Upped CO2
Upped Phosphate and Potassium Dosing
Reduced Lighting
Physical Removal
Overdosed with Excel
Three Day Blackout
Overdosed with Excel
Removed hardscape and boiled it
After I had done all of that, no more BBA...ever. Getting nutrients under control is the first thing, this will ensure it won't come back. In my experience, when I got my nutrients under control, the BBA quit spreading, and what was already there quit getting bigger, but it didn't die/fall off the plants/rocks. That's why I moved on to everything else, to remove/kill what BBA was left.