-siphon the cyano, and be very diligent until it starts to get under control
-check rodi tds level
-check skimming efficiency
-check feedings
-water change frequency/volume
-flow flow flow (dead spots spawn cyano)
-test for phosphates, nitrates
-Chaeto in sump.
-a carbon/gfo reactor can also help. For my 29gal, I use a TLF reactor. I fill it maybe 60%. Mix of 80% carbon, 20% GFO. I change it as needed based on levels, or every 4 weeks. Whichever comes first. Tip: Mix the GFO and Carbon. Don't layer it! This helps prevent the GFO from clumping and clogging the reactor. If you use two reactors, then you can more easily control GFO 'tumbing' and reduce the risk of clumping. Harder to do with multiple media in a single reactor. If no reactor, a filter sock can help, but it doesn't work as efficiently as a reactor. Honestly, I didn't find carbon and gfo in a sock very effective. The reactor, yes.