Abstract Eutrophication often results in blooms of toxic cyanobacteria that hamper the use of lakes and reservoirs. In this paper, we experimentally evaluated the efficacy of a metal salt (poly-aluminium chloride, PAC) and chitosan, alone and combined with different doses of the lanthanum modified bentonite Phoslock® (LMB) or local red soil (LRS) to sediment positively buoyant cyanobacteria from Funil Reservoir, Brazil, (22°30′S, 44°45′W). We also tested the effect of calcium peroxide (CaO2) on suspended and settled cyanobacterial photosystem efficiency, and evaluated the soluble reactive P (SRP) adsorbing capacity of both LMB and LRS under oxic and anoxic conditions. Our data showed that buoyant cyanobacteria could be flocked and effectively precipitated using a combination of PAC or chitosan with LMB or LRS. The SRP sorption capacity of LMB was higher than that of LRS. The maximum P adsorption was lowered under anoxic conditions especially for LRS ballast. CaO2 addition impaired photosystem efficiency at 1 mg L−1 or higher and killed precipitated cyanobacteria at 4 mg L−1 or higher. A drawback was that oxygen production from the peroxide gave positive buoyancy again to the settled flocs. Therefore, further experimentations with slow release pellets are recommended.