Yes sometimes it's a control method not a permanent kill. The benefit for you is the length of time in between kills where you coral and tank is not ravaged by the algae
You can find better preventatives in between each kill.... Ideally you would lift out the coral and set it on a dinner plate
Have a little spray bottle of clean tank water
Wet paper towel squares with peroxide and wall paper them around the skeleton, which keeps peroxide off the polyp, a clean application method....
Spray the polyp occasionally to keep it wet, sitting on the plate for four mins, kept moist, then put back in tank will be fine. Four mins of really wet paper towel, or paint brush application will be a much more aggressive kill.
Also don't forget the option to hold the polyp upside down in the tank where the skeleton area with the algae sticks up out the top of the water. You can peroxide burn it for 30 mins that way if you want, sometimes the most creative approaches are the simplest. Make a little styrofoam raft to float it for awhile, so many different ways
If the polyp is wet the whole time you can focus on treating the exposed part without concern.
Imagine how far gone the coral and others areas might be now if we never took the first action. What you have used to kill thousands of tanks because nothing could stop it. If your worst case outcome is you retreat every three months until a miracle cure is found that's ok!!
Toothbrush wet w peroxide is a fine approach.