MPS effects?

[AClogston]

We've been using MPS for a couple years as a weekly maintenance shock in the pools at our hotel, mainly due to the "swim in 15 minutes" claim. We have a 35,000 gallon chlorine pool outside and a 25,000 gallon bromine pool inside. Still, I was curious about the effects and possible interactions involved when using this product.

According to my CPO handbook (just got it this week and take the test in April, hence my discovery of this fantastic website!) MPS interferes with Combined Chlorine readings when using a DPD test. If CC is TC - FC, does MPS effect TC or FC since the CC isn't directly tested? Or does it slightly effect both? Does it effect bromine readings at all?

I also had another question about using it in bromine pools that I asked in another thread but it wasn't quite answered. If I use MPS weekly in my bromine pool and an "incident" occurs that requires a CalHypo dosing (which hasn't happened in these couple years, thankfully), is there any interaction between the two? I've read in a couple different places you should never use one in the pool if the other was ever used in it. Is this fact or fiction?

I'm going to be switching to CalHypo in the outdoor pool I think, but it seems to be easier in the indoor.

Thanks in advance, this site is a great resource.

 

[JasonLion]

On the DPD test, MPS will count towards the TC level, and not towards the FC level. It will also count towards the bromine level. MPS doesn't normally last very long in the water, so this is not usually a problem. However, if you use enough it can hang around and affect the test results. There is a reagent you can get, R-0867 Deox Reagent for Taylor test kits, to neutralize the MPS so it does not interfere with the test results.

Both MPS and cal-hypo, when used with bromine, will first act to reactivate the bromine. When used at shock levels, and assuming the bromide level (bank) isn't too high, they will both also act on their own to a reasonable extent, because they will only be partially used up reactivating the bromine. MPS on its own is more effective at lowering CC levels than cal-hypo used on its own. The extra CC reduction tends to be especially useful in an indoor pool, where CC is more of a problem. MPS also returns to safe to swim levels far more quickly than cal-hypo.

Of course MPS is not a sanitizer, and cal-hypo is. When used with bromine this doesn't matter as both reactivate the bromine, which is a sanitizer. When used without bromine, the residual FC level left by cal-hypo can be helpful or annoying depending on the situation.

There are no specific problems with using MPS and cal-hypo in the same pool. I wouldn't add them at the same time, or within perhaps an hour of each other, but that is just a generic don't add different things at the same time rule. Cal-hypo will raise the CH level over time. If your CH level gets too high there could be problems. MPS adds sulfates. When used in very large quantities over a long period of time with minimal water replacement the sulfate level could eventually build up enough to be a problem for a SWG cell.

 

[AClogston]

Thanks for the reply Jason. Based on your response about MPS being better at lowering combined chlorine levels than cal-hypo, should I just stick with MPS for the outdoor (chlorine) pool's weekly shock maintenance and use cal-hypo just for "incidents"? Or is there a better reason to stick with chlorine-based shock for the chlorine pool, as I've been told before? The CH increase with cal-hypo isn't really an issue as I have to periodically add some to all the pools anyway.

 

[chem geek]

As for irritation, there is an impurity of 3% potassium persulfate (peroxydisulfate) in the product that is the primary source of irritation for some people and it can take more than 15 minutes to dissipate. It would probably be best to add the MPS at the end of the day to give it all night to work on oxidizing accumulated bather waste (mostly urea) since it will most likely be used up by the next morning before the pool is opened again.

I'm currently double-checking with Dupont, but I believe MPS will oxidize urea which is something that chlorine does only very slowly so in higher bather load pools urea builds up and is the cause of background chlorine demand (i.e. overnight demand after bather load has stopped) and also contributes significantly to the disinfection by-product nitrogen trichloride (trichloramine). So use of MPS or other supplemental oxidizing system (such as ozone) can be useful in higher bather load pools to keep the disinfection by-products lower, especially in indoor pools where there is no sunlight.

As for outdoor pools, the UV in sunlight helps to break down organics and combined chlorine better and there is better air circulation to remove volatile disinfection by-products. So there may be less need for regular shocking even with higher bather loads, though there is certainly nothing wrong with your using MPS overnight in those pools as well if you find the background chlorine demand rising or combined chlorine levels getting too high. Mostly just make sure the Cyanuric Acid (CYA) level isn't getting too high -- for a commercial/public pool with high bather load, there should not be any need for it to be higher than 30 ppm.

 

[AClogston]

MPS doesn't contribute to a rise in CYA does it?

 

[frustratedpoolmom]

No, MPS has no CYA in it.