Get a sea hare. They love eating hair algae.
I would:
1) rip out by hand & strain out with a net as much hair algae as possible.
2) do water change to remove more strands from your system
3) add sea hare to keep the hair algae under control
Other than adding another Phosban reactor, I think this is a cost effective means of getting the hair algae under control. With the RO & DI systems and minimum feeding, you are already tackling potential sources of nitrates & phosphates.
In that size tank, you can also consider adding more tangs or rabbitfish (algae eaters) to the system.
My 210g mixed reef has 9 tangs & NO hair algae.
Hope this helps.
Anthony