Safe Mps Level

[trigear]

i was reviewing some alternate sanitation systems and came across what seems to be high levels of mps use.

For example Cleanwater Blue states to use 1 to 2 teaspoons per 100 gallons after each use.

I dont like blanket statments like that. But if I use my spa 2 times a day it seems that this would be excessive. What do the water chemistry gurus think of this.

What is a safe level of MPS anyway?

[chem geek]

The Nature2 Owner's Manual uses a dosage of 1 tablespoon per 250 gallons or 1.2 teaspoons per 100 gallons. This is roughly equivalent to 4 ppm FC of chlorine. This is not an unusually high amount.

As for how much is actually needed to get rid of bather waste, the rough rule-of-thumb is that every person-hour of soaking in a hot (100-104F) tub needs around 7 teaspoons (2-1/3 tablespoons) of non-chlorine shock (43% MPS). If it is just you soaking for 30 minutes, then that's around 3-1/2 teaspoons after each use, independent of spa size.

MPS is not unsafe at higher levels (in the ranges you are talking about). It is just an oxidizer so will tend to become more irritating at higher levels, but it's not like there's a magic number where it becomes unsafe (unless you eat/drink it). If you are adding it after your soak, it shouldn't matter much anyway since it will likely get mostly used up oxidizing your bather waste before you next soak. The Nature2 level that is roughly 4 ppm FC equivalent is for sanitation levels that passed EPS DIS/TSS-12. Note that these are levels done before the soak as well as more non-chlorine shock added afterwards. Most people, however, just add sanitizer/oxidizer after their soak. I would say that so long as you add enough oxidizer after each soak so that you still measure some residual (equivalent to around 1 ppm FC or so) before the next soak, you are OK though that is not the official Nature2 instructions since technically you aren't killing bacteria during your soak (so it doesn't prevent person-to-person transmission). The official sanitation requires such killing during a soak which means soaking in a sanitizer during the soak (which can be irritating to some; with chlorine it usually means smelling chlorine and disinfection by-products, mostly monochloramine).

Richard