Thanks for the write up! I knew that MPS could not be used solely as a sanitizer but knew it helped. My tub (Hot Springs Jetsetter) is less than 6 months old, and was rarely used until recently. It was incorrectly used without FC for a while (lately) and the water stayed extremely clear, then I started learning about how quickly the FC gassed off...and now I am maintaining FC. So with that being said I do believe the ozone is working as of right now.
Rather than complicating the chemistry further with sulfates I would rather just replace my ozone generator once a year or so if I can do so myself or even get an aftermarket better generator.
Generally it's not easy to replace the ozone generators as most of the devices stuffed inside a hot tub are not easy to get to. You might research your specific brand of tub and see how "serviceable" the ozone generator is.
"Use of MPS can cut chlorine use nearly in half in most circumstances." - Does this mean that MPS reduces consumption like a stabilizer, or makes FC more effective at lower concentrations??
Neither. There is no reaction between the two for the most part. When you use MPS and chlorine together, you're just using two different forms of chemical oxidizers. So if you use some MPS to breakdown bather waste, then you need less chlorine since there's now less bather waste to deal with.
This POST has some useful rules of thumb when it comes to chemical dosing.
"...to help breakdown bather waste BEFORE chlorine is added. So it's best to use MPS right after people are done soaking..." - Aside from my baseline of FC between uses I add liquid chlorine before I use the tub, so I am not sure when to use MPS if I were to choose to. You say to use it BEFORE chlorine but AFTER a soak, so maybe I should use it once a week after a soak, then shock it with liquid chlorine the following day?
Speaking as someone that does not like soaking in hot, chlorinated water, a lot of people I know with tubs let the FC drop before soaking and then dose with chlorine after they get out. This way, the water is sanitized prior to use but there's no excess chlorine around during their soak. In that scenario, if one wanted to use MPS, then one would first dose with MPS to breakdown the bather waste and then add chlorine about 8-12 hours later to bring the FC up to appropriate levels. The more in-depth reason to do it this way is to avoid the formation of organic chloramines. Bather waste is going to be composed mostly of sweat and urine. Sweat and urine contain urea, arginine, creatine, creatinine, etc. When those compounds become oxidized by chlorine, organic chloramines are formed and those organic CCs tend to persist in the water for long periods of time. MPS is an oxygenating shock that breaks down those organic compounds into much simpler forms of carbon and nitrogen waste. Those simpler forms of oxidized waste can then react with chlorine and form mostly inorganic chloramines (monochloramine, dichloramine and nitrogen trichloride) which are easily gotten rid of over time as they either oxidize further to nitrates, nitrogen gas and carbon dioxide OR they outgas from the water.
But, as you can see, dosing first with MPS then with chlorine can be a bit of a pain as it requires two steps. So I think most people go the other way and and use chlorine on a daily basis and then shock with MPS each week. However, once organic CC's are formed, they are much less susceptible to MPS oxidation.
