Thanks tjm9331I want to say it's diatoms but its hard to tell really.
I'll someone with more experience chime in, I'm sure someone will be able to tell you for sure what it is.
Yes, I did 20% water change yesterday with RODI (TDS=0) after cleaning hair algae. And add 500ml of Seachem Phosguardtrue that why I wasn't sure.
Have you added anything to the tank recently either chemical or physically?
I'm pretty sure diatoms are not just when your cycling I think they will show up when ever there is excess silicates in the water
What do you use for water changes? tap or RODI?
Thanks madweazl,Can you take a pic with the blues turned off?
Thanks mcgyvr,Pic is so... psychedelic but are you sure its not just the hair algae growing back?
And do you have results of a phosphate and nitrate test?
Thanks fishgateCould be coraline if hard, but if it comes off easy probably cyano.
Great adviceHave you tried a 3 day black out? No matter the type of algae a black out will help it get under control. I think it maybe dinos but the photos aren't great for me to say for sure. Regardless, if it was my tank, I would feed well do a 20% WC and syphon out all I could, then cover for three days and see if it drastically helps. 3 day will not hurt your corals, will they be mad? Yes, will they die? No. If it is dinos or calothrix, this should clear it up the first time (you can repeat after one week if needed) if it is ant other algae it will help get it under control, while you fix what you think may cause it.