However, it is important to realize that as bacteria, it is not photosynthetic and requires something other than light in order to start the process...in this case, some kind of nutrient in the water that is in excess of the tank demands. The most common culprit is actually a large influx of a certain nutrient all at once. (i.e. your nitrate level spikes from 5 to 25 ppm in 2 days). Could also be a slow buildup that is neglected, and then gets out of control. Personally, I'd go for a combo of the dark tank, after syphoning it all out of the system.