Are u having bryopsis ?
do note that Bryopsis is different from the regular hair algae which is caused by nutrient.
Recently my tank kena bryopsis too. No matter how much i pluck etc , will grow back damn fast. No fish/tang will eat it. Not even snails. 15% wc / week religiously doesnt even help 1 bit.
Bryopsis can thrive well in low nutrient system. I dont have nutrient issue yet this damn bryopsis grow like weeds.
If you identified your algae is indeed bryopsis, you can try using the magnesium method by raising your magnesium to 1700-1800 with continuum mg or kent marine mg. (Must be liquid , not powder)
I am still in the process of getting rid of this fully. But here is the results of raising mg with continuum mg
Before
After
Only 2nd day dose , some part of the algae will turned transparent and then melted off.