I support the above approach though would remove the rocks. I once killed off a lot of plants doing this... I suspect I used a lot of glut before I was done spot dosing. Also if you remove them, you can give them a lot more abuse before returning.
I have removed some of the surface rocks but the main/large are all sub-soil surface so and sitting on the stone below so can't really be removed. I started dosing/fogging with 10ml Excel on Sunday and so far has shown good results, I would say BBA is down by about 60% so I will continue with it while its working...
For the taller rocks, drop water level to 20-30% (if you only do 50% water changes, find your comfort level ... I regularly do 80% water changes), measure out the appropriate Excel dose and apply directly to the BBA in rocks, eg, syringe etc or controlled spray (you don’t want to accidentally direct spray any livestock), wait 10-20 minutes (again depending on livestock response this can be longer/shorter, obviously longer exposure is more effective against stubborn (well established) BBA)
If you notice a large die-off in any type of algae, some large water changes are recommended to remove byproducts form algae breakdown (sometimes it’s just oxygen consumption so take steps to optimize oxygen levels in tank)
Once visible BBA is gone, I’d continue treating rocks a couple more times (eg, every 2-3 weeks over some months) re cracks etc in this rock surface
As the BBA seems well established, I’d expect to rigorously pursue BBA for the next 6 months, then gradually return to a more general (relaxed) maintenance routine