Kents Phosphate Sponge. Works amazing. Turned my green hair algae into white hair algae and within 3 days was gone from my sand bed. Use as directe, more does not mean better. Remove from water after 24hrs and replace with new if algae is not dying. Best stuff I've ever used and now will only use if needed.
What are your water test results? Are you using rodi water? I would not recommend doing anything untill you find the cause. There are other options to get rid of hair algae.
Never trust what someone else says, always test yourself. My lfs told me there water tds was no higher than 7, my tds meter showed 39. From that point i bought my own rodi and called it a day. That's when i was having my algae issues. Now i have none. You can treat now because either way its a problem that needs to be fixed.
Weekly water changes with properly filtered ro/di until your parameters are in line will get rid of the hair algae. No magic pill or product will work long term.
I dose 1ml hydrogen peroxide per gallon of tank water. Worked on my 40b. Doing it now on my 120g to prevent gha from taking hold. Also agree with good Rodi and water changes. I also have a sump full of chaeto.