theres a pretty simple formula for algae and its based on your tank volume, not what guessing test kits might report on a given day regarding phosphate and nitrate.
the formula is this: anyone willing to spend on reefing can spend 25$ at home depot for a brute can.
a brute can holds about 50 gallons, so that means if someone owns a reef of 50 gallons and below that can be drained off into the bin, giving us direct access to sand and rock for algae killing, not starving. we'd put back water into a clean reef. we wouldnt dose meds, kill off algae, add to compounding in the rocks and sand, which is all other methods. we wouldnt add a cuc to turn the algae into whole waste, we're opposite of whole waste in the moves above.
if your tank is bigger than 50 gallons then usually there are too many excuses/reasons they can't wont drain, so the algae stays and 90% quit. 50 and below we can fix easy, 50 and above you need resolve to fix.
direct access not via the water is one thing you havent tried and we have ten years of threadwork handy to show how well it works. consider taking apart your tank and cleaning it, vs doing the other things which add to waste loading / algae fuel. i see we have double threads same topic, if not taken this post will self edit to 0 in a couple mins
furthering the algae formula, about 95% of infestations are caused by the keeper being unwilling to simply kill the algae and clean the system, name the excuse as to why. 95% of people want to have a wrecked tank, though they post they do not. those are usually the most challenging types of tanks to fix, the ones where the owner of the challenge system randomly pick new methods to try that are opposite of what fix threads show.
they choose the dose water method every time, getting clean reefs is like asking people to do their own tooth extraction.