Mixed reef tank hair algae and diatoms out brake, black long spine urchin not looking good

[xDave R6]

Hello can anyone help me I’m having bad luck with my mixed reef tank lately, diatom’s and hair algae have started to take over my tank I have removed hair algae manually and done water changes but still keeps coming back , also my black long spine urchin has lost all his spines and keeps ending up facing upside down . My parameters ar as follows :

300L tank

Nitrate
:2ppm

Phosphate’s
:0.03-0.00 ppm

Alkalinity
:9.2dkh

Salinity
:1.025

Ph
:8.1

Temp
:25

Nitrite
:0.0

Ammonia
:0
Please someone help !!

 

[xDave R6]

Light are on 9hrs a day also