Have they changed the formulation of Phosfree phosphate remover? When I used it last year, I recall that it was fairly thick and dense looking - sort of like heavy cream. This year, I bought some more and found it to be much thinner and watery, sort of like milk diluted - 5 parts water to one part milk. It did cause my cartridge filter delta P to jump up, but the phosphates are still high. I went to the manufacturers website and asked the question, but they did not respond. So, maybe they changed the formula or I might have gotten a bad bottle.
HISTORY - I have been fighting an algae problem in my pool for quite some time. It has had high phosphate for awhile and last year I treated it without success and then drained over half to dilute it with fresh water. Still no luck so I tested the fresh tap water and even that looks like more than 1000 ppb phosphate. So I decided to retreat with Phosfree. I have added 1-1/5 liters 3 times over the past month or so and the level is still over 1000 ppb.