10 years since our plaster pool was installed. I've been a slave to the pool store and the chemicals. After reading your pool school and a lot of posts I'm ready to change the way I do things. This year after opening the pool it looked great but would not register chlorine. The pool store told me I had phosphates which I never heard before? Apparently not an issue! I found a high level of ammonia on my own and added a bunch of bleach to bring that down. I decided to drain a third of my pool and get some fresh water and ordered a nice test kit based on pool school. I will be throwing away my Nature 2 filter. All the shock Chemicals I have and switch to bleach. Can't wait to save time money and say goodbye to the rip off pool stores!!! Thanks!