Budsreef;770599 wrote: Algae and cyanobacteria are usually a function of light, flow and nutrients. You may have enough flow according to GPH but if it is not hitting the trouble spots you may want to add some smaller power heads to get flow to the affected areas. If you have good flow in the affected areas, then think about your lighting schedule as far as how long during the day the tank is lit, and/or is any part of the day allowing sunshine to hit the tank. Also the age of bulbs can be an issue as well. For nutrients, look at how much and how often you are feeding the tank, do you have any way to export nutrients through macro algaes? If not then you need to do it with water changes. Do you have a good clean up crew? They can't usually take care of algae if you have a major issue with any of the three items but they can help keep it clean if you can correct the issue or issues causing the algae in the first place.