You should find someone with a hanna meter/checker that can check your PO4 levels for you, the test kits really aren't that accurate.
Special Blend is a bacterial additive. I too have found it to work quite well in clearing up cyano.
10-4. I'm meeting up with a member this morning and am going to give him a sample of my water to take with him to have it tested, hopefully something will be found.



