So I took this just after I'd drained my pool. The pool water had not been drained in at least 25years, maybe longer. Apparently, after so many years of backwashing and evaporation, the pool gets a build up of cyranuric acid, which does not allow the chlorine to work correctly, so you get algae build up and are constantly adding shock. The only way to remove the cyranuric acid is to drain the pool completely. Makes for a large water bill, that's for sure! Decided to have some fun with the rest of my backyard with the processing . Oh, the pool took about 16,000 gallons, and looks fantastic now!