Shocking MPS question!!

[gores95]

Like most on this board I have added dichor daily after each soak and shocked weekly with MPS.  Our tub was delivered on 10/17 and I have still not changed the water...so far no issues and the water is clear with no foam/rings, etc.  That being said I am probably going to try to change the water on Sunday when temps could approach 50.  One question on shocking though.
 
Here is what happened with my tub in the last day.  I added 2 tsp. Dichlor yesterday early afternoon after soaking and today (about 20 hours later) my FC was .5  and my TC was 1.5 (CC is 1).  I just shocked with MPS and about 15 minutes later my FC was near 0 and my TC was also near zero.  What should the chrlorine numbers look like after shocking?  I know people here leave their covers off after shocking so I am assuming the chlorine levels go up?  Also when should you shock...right after adding the daily dichlor dose or wait until the next day when the chlorine is near zero?
 
FYI I usually leave the top open for 20 minutes after adding dichlor/shcok and I use the Taylor test kit 2005.
 
Thanks,
 
Marc

[anne]

Here is what happened with my tub in the last day.  I added 2 tsp. Dichlor yesterday early afternoon after soaking and today (about 20 hours later) my FC was .5  and my TC was 1.5 (CC is 1).  I just shocked with MPS and about 15 minutes later my FC was near 0 and my TC was also near zero.  What should the chrlorine numbers look like

I was curious about the same thing a while back. The majority response I got was that the CC *does not* convert back to FC when you shock with MPS, it is just oxidized and destroyed, so it is all gone. So it makes sense to me that your CC went for 1 to zero. I cannot explain why your FC went from 0.5 to zero. I did not think that MPS "ate up" free chlorine, but perhaps soemone else can clarify that. I would suggest that either the MPS interferes with the chlorine reading (though I think if anything it'd give you a high reading), or, was there enough time passed between the first and second chlorine readings that the chlorine could have just dissipated?

[gores95]

Thanks Anne!  Do you know why we all leave our covers open after shocking?  Perhaps to allow the oxidized chlorine to dissipate?

[Ehizzle]

The MPS does give a false chlorine reading, usually high. But, depending on how long between tests and if you were shocking with the cover open, Chlorine is heat dissapated and probably just went away. You should not expect an accurate test right after shocking though. We leave the cover open, yes for the oxidized chlorine to burn off, but also so it doesnt oxidize the cover.

[tileman]

Like most on this board I have added dichor daily after each soak and shocked weekly with MPS.  Our tub was delivered on 10/17 and I have still not changed the water...so far no issues and the water is clear with no foam/rings, etc.  That being said I am probably going to try to change the water on Sunday when temps could approach 50.  One question on shocking though.
 
Here is what happened with my tub in the last day.  I added 2 tsp. Dichlor yesterday early afternoon after soaking and today (about 20 hours later) my FC was .5  and my TC was 1.5 (CC is 1).  I just shocked with MPS and about 15 minutes later my FC was near 0 and my TC was also near zero.  What should the chrlorine numbers look like after shocking?  I know people here leave their covers off after shocking so I am assuming the chlorine levels go up?  Also when should you shock...right after adding the daily dichlor dose or wait until the next day when the chlorine is near zero?
 
FYI I usually leave the top open for 20 minutes after adding dichlor/shcok and I use the Taylor test kit 2005.
 
Thanks,
 
Marc

Whats up Marc.

Since I'm always right you might want to write this down.
I usaually shock my tub when FC is under 1 b/c I feel like I can get a more accurate CC reading. When I use mps to shock, I add the recommended 2oz per 250 gal of Renew and this has been working for me. I don't check any chlorine levels for 1-2 days b/c the shock dose of Renew really skues the readings. I add my daily dichlor along with my mps shock. The reason you leave the cover open after shocking is to allow the chloraminates to escape into the air and not your cover, pillows, etc. The time you leave it open will be longer when you superchlorinate opposed to the mps shock for the obvious reason that dichlor raises FC and mps doesn't.

[gores95]

Very cool.  Thanks guys!