Green hair algae

[rebecca_nano_reef]

Hi everyone, my fluval evo 13.5g has been set up 9 months. 2 months ago I added a new large piece of dry rock. The last 4/5 weeks I’ve had hair algae on that rock. It was pretty bad but managed to get rid of most with flux RX. However all my parameters are good. Phos 0.05, nitrate 9, alk 8.1, ph 8.2.
Why is the hair algae growing back? It’s getting frustrating now. I’ve turned the white lights down to 25%.
What can I do to stop it reoccurring? TIA

 

[THE REEF WHISPER]

Nice tank I have the same tank I can't keep torch Corals or hammer or any lps which is a bummer my tank won't let me only ducans making it a bubble tip and soft corals mostly mushrooms high end and stock it full of them doing that soon