Hello, I am a "retired" jack of all trades/master at none who works part time (now that I'm retired!) at an afterschool program for "at risk" kids. I have become the caretaker of the facilities. I do anything from IT work to cutting the grass. Our facility has a 100k gallon pool that was installed in 2003. Recently I was told that I needed a 3hp Pentair Whisperflow pump replaced at $1700 (after YouTube and some checking around I found that all I needed was an impeller and a new gasket kit -$140 and I had it up and running again) My pool guy is telling me I need to replace the sand in my filters, ( it's been there for 6 years) but after coming here and reading some threads I find that this may not be true. So...since I'm now apparently adding "pool skills" to my current list of trades that I don't currently master, I'm looking forward to learning about chlorine, ph, ionization systems (we have one of those that hasn't been running for years) and my Aquasol systems (which currently is running) Whenever I go to local pool companies for answers I come away with many different opinions. I'm looking forward to talking/searching out information and problem solving here. Thanks in advance for all the help and advice!