It certainly seems that you do have about 40 ppm of CO2 and good water circulation. I haven't read anything I can recall that suggests that potassium in any quantity leads to any kind of algae. As far as BBA on hard surfaces in the tank goes, when I get BBA it always hits those surfaces as bad as any other in the tank. The only other thing I can think of is routine weekly cleanings - doing those well is also good insurance agains algae attacks. With that I have shot my last arrow!