Ye 0.03-0 phos….I run rowaphos 24/7 and it will remove silicates and also phosphate which should help get rid of the diatoms and remove phosphate which GHA can use as a food source (and give you a false zero phosphate reading, I assume you mean 0-0.03 not .3)
It looks like diatoms and a little cyno bacteria to me from the picture, so the above will help, but try and increase the flow in particular to the parts were the cyno is forming
I wouldn’t let the nitrate get any lower (than 5) and there’s nothing wrong with 10-20. Cyanobacteria love low nutrient environments
And with those corals, and your nutrient levels, you could probably dose reef energy every month if that. I use it/reef roids about once every month in a 2000 litre full blown reef.
Ok I’ll cut back on the roids and a+b…..
As for the corals not opening, thinking it’s because of the diatoms…… Any idea how long they can stay closed for without any issues?