The cyano will use the nutrients, thereby reducing them. Is it on the sand bed, the rocks, everywhere?
Adding some additional flow the area and siphoning it out can help. It cannot take hold in area of adequate flow (supposedly).
Cyanobacteria is brought on from excess nutrients, low water flow and the wrong spectrum lighting can add to the problem also.
Just to go through the litany once again:
1. cut back the lights to 4 hours or less /day
2. cut feedings to every 2-3 days
3. cut amount fed at feedings
4. continue to do 20% weekly PWC with RO/DI water
5. vacuum out the cyano during a PWC
6. test water for PO4 and it tests above .03 start using GFO, Phosban or similar
7. test for nitrate and get 0 for a reading
8. replace all bulbs (PC older than 6 months, MH over a year, etc.)
9. add or move a PH or two to achieve more flow in the affected areas
As a last resort: Chemi-clean by Boyd Enterprises, Inc. It will take care of the Cyano in your tank in just a few days. It is reef safe.