MPS: can I still test chlorine levels?

[wkussmaul]

I used MPS to shock my spa recently; Now the chlorine test is off the charts high.

1) So must I use a special test kit for chlorine when MPS is present?
2) Without the special kit, is there still a way to keep track of FC and TC levels?
3) If I stop using MPS, does it wear off so I can go back to just using my SWG and occasional added bleach? Or must I drain and refill?

 

[JoyfulNoise]

If you plan to use MPS often then it pays to get the interference removal reagents. Otherwise, just give it a few days to “burn off” and get back to normal. It eventually converts to sulfates which do not interfere with the test.

 

[JoyfulNoise]

But do note - sulfates are bad for SWGs. Most SWG manufacturers have strict warnings about not using dry acid or MPS with an SWG. So you really don’t want to use them frequently if you plan to run the hot tub as an SWG tub.