I may have as much or more experience with alge in fuel. Get the biocide from a store that deals with marine products, West Marine is one. Fishing boats deal with alge often enough. The biocide added at the refinery is not good enough sometimes.
The Slabs, fire lookout, bottom of a gravel pit,truck parking lot with armed guards in El Paso. Next to a fenced pioneer grave in the desert, Jaw Bone Canyon in the week after Xmas with hundreds of dirt bikers.