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Three steps:1.power off to spa.2.drain and scrub out spa.3.refill and reheat spa.I have told my customers for two decades now: water change at the end of the first month of ownership. Also: water is the cheapest (and most effective) chem you can add to your spa.
What if you try switching to di-chlor granular chorine. put 1-1.5 tsp evertime you get out ( or 2-3 x's per week.) and use your MPS as a suplement to that and use it once a week.This will give you a boost immediately after you get out when you need it most and by the next time you get in there will not be any chlorine odor.I would think that this would help eliminate the scum.
I initially had scum problems, then started doing just what saledvl suggested. Now the only scum problem we have is shown below.
this spa is driving me nuts.
Oops, Thought this was a Haven Thread