Hair algae in my media reactor?

[Blakskall]

I have little hair algae that forms everytime i change my gfo in my phosban reactor, but it doesnt really appear in my tank, and my levels are fine, any explanation for this?

 

[nuwave59]

Do you have a fuge with lights on next to it?

 

[Blakskall]

No fuge, its hob style in my tank

 

[Blakskall]

I dont understand it :-(

 

[Blakskall]

I was thinking, could this a indication of the gfo asorbing all the phosphate it can and its done? My nitrates are running very low on my test kit, but the phosphates are undectable, so obivious the algae is eating them