A cycle of diatoms and GHA are pretty common in a new-ish system. In my experience, when I try to increase nitrates, green hair algae (GHA) is the first thing that responds. It'll start growing and take up all the nitrates so my levels still show as being pretty low. I've always viewed taking the rock out and scrubbing it as a last resort but that's just me. Post a pic of what you're talking about but I'd be tempted to let it ride and try to get rid of it over time. Any drastic moves at this point might lead to the system taking longer to smooth out and stabilize. FYI - I'm dealing with the exact same issue in my frag system that I set up in early September. Low nitrates, dosed nitrates, GHA showing up and what I describe is exactly what I'm doing. To combat it I picked up some additional blue legs and a Tomini Tang. Other than that, I'm going to let the tank look ugly until the point that frags start being effected. My goal is for the system to tell me what it needs and drastic measures are effective at getting rid of the exact issue but but not so effective in reaching long term goals.
I'm using my 65g display as my example. That system has been up and running for 10 years and I can usually tell what I need to do by looking at it. Algae coming in a bit quicker than usual? I do a water change. Coral looking a little dull? Hold off on water changes. I compliment my "eye testing" with real testing too but the tank is so stable that I'm rarely surprised by the readings I get. I've had GHA take off in the system but have always been able to get it taken care of before it gets outta hand by water changes. It takes a little longer but it's been a better solution for me long term
