Cyano part of new tank break-in?


Reefing newb
In the fuge section of my sump there's not a lot of flow going through it. Over a few days what rock I have in there gets pretty much covered in red chaeto. I do have a light over the fuge section and it's on all the time. Maybe I should cut it down to maybe just dark hours? I put a spare small powerhead in that section to get the water moving around so it doesn't build up as good but just wondering if the cyano growth is part of the breakin-in of a new tank. It's been post-cycle for three months now and I know most algae shows up then just dies off as the tank gets better at killing it off.
If you have cyano in the sump I would syphon out all you can and kill those lights for 3-4 days. If that kills it off and you want to run a sump light then time that light opposite your display lights.
I now have a good bit of cyano in the DT as well as the sump. I am now wondering what route I should go about removing it. I have 35 gallons of water ready for a change but I don't know if I want to do a total blackout for three days then do the water change, use the chemiclean I have (I have used this before on other tanks) and put that in, black it out for three days with skimmer off and do the water change then or just try to suck out what's in there now during a water change and run the tank as normal. I don't want this to get any worse than it is now so I need to decide soon. What's the best route?