I purchased the TK-100 kit 4-years ago and have been very pleased! My pool has remained crystal clear using the Trouble Free Pool philosophies. I live in winter climates (Wisconsin) so I drain down about 2-ft each year to get below jets and winterize. In spring, I fill from hose back up to level. That said, my water is getting about 4-years old now… wondering if I need to test for anything else? I have “well-water” so do I need to be aware of anything that might be creeping up slowly? I do have some iron in my water (I treat that with my water softener-inside house) but have not seen any signs of that in my pool, not sure if I test for that or not…since my pool has been over the years in perfect/near perfect balance. I usually test my pool every other day so I catch stuff early before stuff gets outta whack. When kids are using constantly and air temps are soaring over 90 I check daily.
I use the Pentair Clean and Clear plus 420 Cartridge Filter system if that's of any relevance and my pool is a (inground) chlorine water pool. Roughly 30,000 gallons. All my equipment is Pentair - zero issues.
Thanks for any input!