I have a suspicion that the hair algae is trapping its own food and therefore whilst phosphate in the water is okay the algae has its own personal source!!!

I am going to up the number and variety of grazers as well as the flow rate so hopefully that will fix it.

My RO product water has a TDS of about 3.

I forgot to add that I have a sea urchin in there too which is effective when it gets to a rock with hair algae it just doesn't move around enough seems to be happy going around the same bunch of rocks for months on end it only goes at one end of the tank. I'm thinking off getting another one to put at the other end of the tank in the hope they will have one end each weird things urchins!!!!

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Alan

Thweeerp!