Our giant peroxide threads ranging 60+ pages would be a headache to find a comparative tank for your issue
I'm aware of the algae fix marine it is valid to try and similar to peroxide in affect but there are still measurable slight differences
I have something that w give you a much better fighting change between the two, whichever you choose
For both, dosing the whole tank from the top is the last thing you would do. That treats targets and non targets equally so it stinks, although it works on many invaders anyway.
Here, we can see you have a totally nutrient independent invader. For this, invasive dinos, invasive macros, valonia, and many more there is no underlying cause, low po4 won't redo an invasion of those on most tanks, to any degree large cure threads can be collected to show results. Import equals invasion. These are direct kill, or direct grazer targets for sure.
You want two things here in your chemical ventures:
Non committal test areas
Submerged concentration dosing, not top water dosing per unit of volume
I'm picturing your home sized sps being mine, ever so careful to not RTN that whole tank...lower the photoperiod imo or diffuse the intensity down a bit during this treatment. Less intensity during treatments
For sure do nothing that could cause an untoward alk spike while dosing any oxidizers for sure
Be creative about contacting your doser to the target even if briefly, it beats top water dosing always. It can be as simple as using syringes to inject slowly right onto the patch, using underwater Saran Wrap pinned into place onto larger areas of the targeted rocks where accessible, system pumps off of course, and inject up under that. Whatever chem you use, amplify it to the target, and downplay it to the corals.
Even though its no small job, consider drain and treats, most sps tanks can be drained hours w no affect especially if you sw mist them while working. Simon Garrats reef that is auto drained for three hours three times a day is an ex
Clearly top water dosing is preferred for large tanks, but before going all out try some non committal tests
Find a rock you can remove easy and dry treat it with our p method just to see what ideals will reveal. As possible lead ins to drain and treats since they attack the sps the least of any situation where removal isn't an option....shoot a test rock with external algae fix marine as well to get full breadth comparison.
What I've seen this last decade while amassing large threads on it was how people will jump the plank and start top dosing full guns without any incremental short tests! Do underwater short testing of both p and AFM would be my offer. Ramp up!
The largest volume tank I worked on in the reefcentral peroxide thread was a 400 gal w invasive macros, they take well to top dosing. Your brush algae prefers emersed treatments for sure, small tests will reveal how they respond to the diluted attack required in such a large tank.
What a challenge we have here I love it. Keep posting pics of your ramp ups man
By all means consider grazer experiments, thats the only way whatsoever the real reefs keep this in check. It is never ever nutrient limited in our tanks or in nature. Direct attack is the only way, I guarantee that. Find the right grazer, luck will ensue
In the meantime, get to cheatin but go slo