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This is my observations during my vast 8 weeks of experience - including two water changes.I use ozone, N2, and dichlor. After I use the tub I raise the Dichlor PPM to 3-5. If I use the tub within the next 48 hours, the PPM is down to 0.5 when I get in and the water is fine. The Ozone and N2 seem to keep the water clear that long. If I go beyond 48 hours without adding more dichlor, I have water problems.
It sounds like I do your routine but reverse. 2-3 PPM chlorine after I get out and shock on Sat with a chlorine and MPS type shock.
Remember, you are SANITIZING the spa not STERILIZING it so even at .5ppm, there will be bacteria. With Nature2 and ozone, you still need to get the level of chlorine up to 3-5ppm, it will just take less chlorine to do that so they say. It is a very hard thing to prove. Basically, if you follow the rule:3-5ppm after each use and never go more than 4 days without chlorineyou should be all set.