I am dealing with a baptism tub, set up like a hot tub last year, with a UV sanitation along with non-chlorine oxidizer and a Algestat. everything works well with balancing the water each week using a powder form of PH down . We use it approximately once per month, and keep it ready for immediate use (90F) at all times. the only issue is calcium build-up on the fiberglass walls and I assume in the heating element. . I drain and clean every three months and let dry for three days before re-filing with filtered tap water. It begins at about 8.5 PH and I adjust down to 7. PH. Still not working to keep from the build up.
Any suggestions could help
