I’m a new spa and pool owner and a big fan of Poolmath. I’m using 3-step bromine method in my spa and have one question re dosing. In other posts chemgeek shares that to get MPS dosing from poolmath, simply double the dichlor dose amount. One caveat is that it assumes 43% MPS. Most of the brands I see online and in store are 36% MPS. My farmers math tells me I should be doing -2.5x dichlor dosing amount from Poolmath to compensate for the concentration difference. Wanted to confirm that here. Thanks!
MPS
- Thread starter Optimus239
- Start date
- Jun 22, 2014
- 47,885
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Welcome to TFP! 
You questions is too much math for me 
so I'm going to ask @Donldson for some assistance. 
He is well-suited to breakdown this issue for you.
You questions is too much math for me so I'm going to ask @Donldson for some assistance. He is well-suited to breakdown this issue for you.
This one is a bit outside my wheelhouse, for the reason I'll talk about below. However, that math is likely close enough. I don't think MPS has any weirdness to it that would require more advanced calculations.
That said, despite the guide including it I would personally recommend against regularly dosing MPS. MPS contains sulfates that will build up over time and can damage the metal in your heating element and the fiberglass shell (if you have a fiberglass tub). Liquid chlorine would be the best option. If you do stick with MPS make sure you regularly change the water to prevent the sulfate level from getting too high.
Welcome to TFP!
That said, despite the guide including it I would personally recommend against regularly dosing MPS. MPS contains sulfates that will build up over time and can damage the metal in your heating element and the fiberglass shell (if you have a fiberglass tub). Liquid chlorine would be the best option. If you do stick with MPS make sure you regularly change the water to prevent the sulfate level from getting too high.
Welcome to TFP!
It is also not unheard of for people to be allergic to MPS, and develop a rash if they soak in it.