Looking for Guidance- Cyano in Sump

[reefbyremote]

My reef is 90 g with a 30 g sump. It is 2 years old and mainly sps. All is going well in the reef but over the past 2 months I have started seeing cyano in the
the sump in the centre refugium chamber (which has about 2 inches of sand and a little rubble rock as well as chaeto.) Cyano has never appeared in my system before. The return pump is a aquarunner 2500 and I am running multiple powerheads in the main tank. I am also running gfo in a TLF reactor using a small powerhead in the sump.

Any ideas on my the cyano is limited to the sump? I presume it is a lack of flow issue or lack of clean up crew? I could increase to a larger return pump or installing a powerhead but would appreciate your guidance first.

Also what does everyone think about dumping the refugium, at the very least the sand in the refugium?

Thank you