I developed the below sanitizing routine over the past 16 years with my Marquis 450 gallon spa and it worked well. I am purchasing a new Sundance 980 Lisbon (370 gallon) and am planning to use the same routine (scaled down by 20% for less water) but want to corroborate with others the science behind what I've been doing. Aside from water health, my goal is to have the minimum amount of chlorine in my water.
My routine:
Nature 2 plus changed every 4 months
Initial Fill Only: 2 tsp of sodium dichlor (3ppm) - wait an hour then add 1/2 cup of MPS
Shock weekly with MPS (3/8 cup = 3oz)
Add 2 tbsp of MPS mid week if heavy use.
Ozonator
This is my understanding of how it works and what I'd like clarification on:
With the initial water fill, the chlorine binds to contaminants and is turned into chloramines. The weekly MPS shock pulls the contaminants from the chloramines and frees up the chlorine to be active again - but in a minimal amount. The Nature 2 does the rest of the job of sanitizing along with the Ozonator. The new Sundance will also have UV.
As I understand it, this method is difficult to detect the level of chlorine (free or combined), so I'm going by the seat of my pants - and water clarity. I also don't understand what the MPS turns into after added to the water and what accumulates over time because of it.
Other tidbits that probably have something to do with the balance, and I'm including just to make sure I've given all relevant info:
My water is naturally soft (10 ppm Calcium) and I have to add a fair degree of Calcium at startup.
My water was frequently basic and I had to add a small amount (1 tbsp) of dry acid to balance.
Alkalinity was always low. If I tried to get above 60 ppm (using baking soda), the tub would get too basic. I chose keeping the pH balanced and occasionally added baking soda to increase alkalinity to 60 ppm.
Thanks in advance for any insights.