I use it to control black beard algae. It doesn't work as well for other types. I got a clean spray bottle, fill it with Excel, or API has an equivalent called CO2
Booster, then lightly spray where the algae is when I have a low water level during a routine water change. Make sure when you do it that you have something moving water, I use airstones. Then fill the tank up and watch the BBA start turning red. That makes it easier to pluck off.
One of my tanks was so badly taken over by BBA that you couldn't see the driftwood. After doing this for 3 weeks (once a week), you'd never know.