very backed up at work having to work in increments:
your tank will be very easy to work with. we need to incremental test it before upscaling and taking full action...that's why this method is ideal, its mini modeled before the big job, and its invader specific. any messing with nutrients is invader + nontarget stressing, we're targeted and much faster
(we/nano keepers who have access

)
notice on your back wall how the tank is aged enough to have accreted fanworms on the actual glass, but no green mess in the corners, along the silicone, wedged into those worms and tufted all over the glass>? that matters hugely in your overall reset methods here. it means your water/nutrients never were an issue or the algae would be located other than the places nature wants it--the rocks.
I get tanks in my message box where the
glass and the rocks are invaded, yours isn't. even if you were scraping algae off glass, its not bad or your silicone and joint areas would be colored up and spotty and dark or green/black but they aren't, your invasion is where nature wants it: on rocks so a parrotfish can happen by and bite it all off, digest the plants, and poop the sand.
you have no nutrient issue in this tank if you are using decent topoff water, your invasion is due to lack of grazing and the peroxide method cheats us into grazing. I recommend hold course with nutrients, sequester no more nor less just hold course where you are and begin actual target work and this tank will comply.
*it isn't forever, its until that rock is purple with coralline, then the algae will stop given all other factors decent and fair and normal. Nature grows algae just like this in
perfect reef waters, and due to that grazers have tonnes of food to eat.
you have no other issue in this tank other than lack of grazers, I would never need to know your nutrients in order to reset this tank and here's how we test that claim and build up some nice turnaround pics for our huge peroxide thread:
incremental testing to assess invader before we nuke it (we are watching for growback potential)
1. take one test rock out and lift it out of the water, and simply pour peroxide 3% from a brand new bottle across a patch of algae hitting no corals. let it sit wet in the air 2 mins, don't disturb the algae on this rock, its liquid-only efficacy testing. rinse this rock off after a couple burn minutes, and put back in tank. the algae w look the same, bubbly perhaps a little, but no big changes tonite. notice in 36 hours how that patch will look though, itll be white and falling off I bet.
2. take a second rock, or an area on the first rock that wasn't wetted w peroxide, and this time
scrape the algae off the rock using pointed and careful dentistry;rasping; just pick and poke out the algae until the knife tip made that area scored free of invader, then put peroxide externally on that spot
after it was cleaned. first spot was no rasping, the hail mary pass, it'll prob work fine. If not, the second test was a scoring/rasping test where the anchor points were literally dug out as a rasper would have done intently in nature, damage some rock while you are at it, this is a mean portion test in case your invader is deeply rooted and grows back really fast, but I predict it wont, and top treatment alone will look great. The rasped rock is worked with metal sharp knife tip to be algae free first, the peroxide goes on the clean spot after you worked it, to wick into any leftover holdfasts because really mean invasions take
scraping to dislodge them, or they'll come back. Even snails and crabs don't rasp correctly, they're mowers, they leave the roots. it takes a rock biter in nature to be thorough, we're mimicking that.
no peroxide was dumped in tank
no non targets were affected here
its not possible to bleach out your corals or overdo starvation here, I literally work zero percent on my 12 yr old nano now on algae control, its purely cutting out stony corals to get them out of the bowl and make space that occupies my time, all you need is to hand guide your tank.
for it to have produced only that much, locally, without any real hand guiding actually means your tank will respond very well to some directed gardening
I have 5 tanks right now in private message getting turned around from this very method. Hotashes is already well past the clear and into the heavy coral stocking method to block out the former real estate that algae wanted. I never ask for, or need to know, anyones nutrient levels for nitrate and phosphate in our turnaround threads, as those items don't determine if you are invaded or not, they determine how much you must manually garden. They're preventative moves, they're not remover moves.
you will be able to see if this works, or doesn't, within a few days and from that you can upscale to the rest of the tank. You can see why this is hard for large tankers, nano keepers are truly spoiled once you figure out you can just cheat kill algae and not have to take months of hoping.
we're literally moving away from an external locus of control reefing system and into a fully 100% self accountable you choose if you are invaded or not internal locus of control system. When we're the grazer, we have final say over how the tank looks, and even though hand-scraping without peroxide is still good and will remove an invasion, it leaves too many holdfasts in place for regrowth, so the peroxide burns that part out and
drastically stops regrowth, as a cheat. when coralline is there, algae will look for another spot to land and set up competition, coralline is powerful. you are awaiting that natural blocker, and you must free up space/real estate from algae so that it can adhere on the rocks, its a guiding process over time.
Its the total complete opposite of hands off approach; a nano reef is best ran clean in the beginning, farmed into compliance, then in its golden years it will run forever without biological headaches.
if your sandbed can produce a cloud if disturbed, that's algae feed, and you may want to clean that. **it affects growback, not whether or not you are invaded as a recurring theme here.
I deem this tank not a nutrient issue, but in need of man grazing, with cheat, stat
I know this is a ton of stuff to type, but we are about to adjust your approach to reefing in a small nano itself, not the algae.