Sometimes cyanobacteria and nuisance algae can be tough to deal with. No matter how many water changes, no matter how many chemicals, no matter how much siphoning, the stuff still persists. One low-budget, well actually money saving, technique that you can use is turning the lights off. Because cyanobacteria and pest algae rely on photosynthesis, performing a simple water change may not get rid of them completely. Once you have taken care of all of the excess nutrients, turning the lights out for a couple days will help you push the dreaded stuff over the edge. All that is needed is two to three days of complete lights out, and you’ll stand a much better chance of finally getting your aquarium clean. I do not recommend using this technique for more than three days, as other photosynthetic organisms (e.g. your corals) also depend on the light. Think of this technique as a last ditch effort when dealing with nuisance algae.