"Cell-bound and extracellular phosphatase activities of cyanobacterial isolates"; Microbial Ecology
; Whitton, et al, 1991.
Toxic Cyanobacteria in Water: A Guide to Their Public Health Consequences, Monitoring and Management
; World Health Organization; edited by Chorus and Bartram, 1999.
The Biology of Cyanobacteria
; University of California Press; edited by Carr and Whitton, 1982.
"Competition between picoplanktonic cyanobacteria and heterotrophic bacteria along crossed gradients of glucose and phosphate"; Microbial Ecology
; Drakare, 2002.
Doesn't really matter whether ya believe me or not, Plantbrain. The literature tells the story.
I'd hafta say ya don't have phosphates in excess of what yer plants are using. Yer plants are well-established and ya have enough light to keep growth at a pace that keeps algae and cyanobacteria blooms under control. If yer also dosing CO2, then the plants have enough carbon to use up the phosphates, leaving nothing or little left to promote a cyanobacteria bloom.
Brian Mc, low O2 levels are a result of eutrophication induced by the cyanobacteria, rather than being a direct cause of the cyanobacteria bloom. Once cyanobacteria get a foothold, they outcompete other microrganisms and higher plants, killing them, releasing more nutrients in the water through decomposition. Decomposition uses up O2. In addition, the reduction in DO can release bound phosphates from organic and inorganic substances in contact with the water into the water column, creating an even larger pool of phosphates for the cyanobacteria to use. It's a self-perpetuating circle. Unlike algae and higher plants, cyanobacteria can photosynthesize in anoxic conditions, so low DO is irrelevant to their continued survival and prevents competition due to plants and algae reestablishing themselves.