Hello I have been battling cyanobacteria for the better part of two - three weeks in my 75g planted. The tank is almost 4 months cycled. I believe the original incurision of it sprang from a low nitrate high organic debris environment with an inconsistent lighting schedule. Due to the scape there was a few rocks I wasn't moving previously to gravel vac and a large amount of detritus formed there. Since then I have been more diligent with removing said debris. Also purchased a timer to create a consistent photo-period (8hr photo period). As well as having a phosphate test kit arriving today to check a phosphate build up off the list (30-50% wc's weekly so I doubt it) Equipment 75g freshwater tank Emperor 400 & Sunsun 304b filtration Air pump running 2 airstones (May begin turning these off in day time to promote better co2) Low bioload Stocking : 2 Honey Gouramis 1 Albino Paradise Gourami 3 Juvenile Angelfish 1 Clown Pleco 6 Sterbai Corys Pest snail colony 1 Assassin snail I have negative Nitrate Creep with current plants Parameter test results Ammo - 0 no2 nitrite - 0 no3 nitrate - 10 ph - 7.2 phosphate - .25-.5 KH - 3° / 53.4 GH - 6° / 106.8 So onto my question / gameplan to battle it. Today I plan to peform some regular maintenance then initiate a blackout. Parameteres check (ammo, no2 , no3 , phosp , gh, kh , ph) Install timer (8 hour photo period) Remove all easily accessible visible cyano via gravel vaccum as well as detritus. Cut all lights - wrap front of tank in black trash bag to prevent ambient light (Plan to cut lights for 72hrs) I have read mixed instructions on whether to dose macros (Potassium Nitrate) into the water column before initiating this blackout. From what I read Potassium Nitrate is supposed to help inhibit BGA growth due to it thriving in low oxegyn / nitrate environments. Potass I'm assuming is to help promote plant growth to out-compete the BGA. After the 72 hours I will be doing another large WC / gravel vaccing to remove any build up during the period. Any one have any suggestions on something I can do differently or an aspect I might be missing? If the 72 hour blackout fails I plan to use a product such as Chemi-Clean or Erythromycin (probably the former). Would rather avoid chemicals if possible though. Anyone have a positive or negative experience with these products?