Don in Phoenix.850 gallon in-ground tiled spa with water feature, installed 1999.
Upgrades: Pentair Intelliflo VSF pump with EasyTouch 4 and ScreenLogic 2 controls.
Pentair Triton II TR-40 sand filter. Hayward H400 natural gas heater. Test kits: Taylor K-2005 + FAS-DPD