Great reply. I was going to post a new thread but someone beat me to the punch on the subject. Appx. Two weeks ago I had phosphate reading of 500 ppb (this was on a Saturday). The following Thursday, I added about 1 1/4 liters of Phosfree. )I have a 15K galloon plaster free form pool. It hasnt been a week since I added it so I take it my water to get tested.. Now the phosphates level is reading close to 1000ppb and I have been more mindful about skimmming the pool and cleaning out the baskets.. Now they tell em to add another liter.. I dont have any problems with algae, keep my pool chlorine level at 3-5ppm.. Am I wasting my $$$ buying this stuff then? Thanks.