I am new to TFP and have learned a wealth of info the last few weeks! We bought a house last year with a 27,000 gallon vinyl inground pool saltwater pool. We had company take care of it last year and made the leap to caring for it ourselves when we opened in May. After lots of research here, I realized that "dirt" from last summer was really mustard algae and it has only gotten worse. I will be using the TFP method going forward, but have used lots of clarifier and algaecide to this point. My biggest concern is what to do about the sand in the filter. The psi is at 18 at its peak and didn't climb when I shocked the heck out of it for weeks about a month ago. I will SLAM soon and am curious if I should start with new sand. The pool is 4 years old, so the sand isn't old enough to need replacing, but I am concerned about whether or not it filtering properly. Any advice is appreciated!