MPS questions

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M

mrhappye

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May 25, 2010
52
Fairfax Station, VA
This year when I opened my pool it was dark green. This was the worst in all the years I have had the pool. I began adding lots of liquid bleach as well as calcium hypochlorite in an attempt to get a free chlorine level. Finally, after several days, I seemed to be getting somewhere. However, I couldn't seem to get chlorine level to hold. I brought a sample to Leslies today and the FC level was 0 and CC was 1, CYA 10, PH 7.4. They told me I had "chlorine lock" and talked me into getting MPS. This seemed counter to what I have read here but they somehow convinced me to get it. I added it and later my FC level did rise, using DPD 1 tablet. I don't plan on using it anymore. Do I have anything to be concerned about? Will there be any residual chemicals from it? How long will it affect the DPD 3 test? I plan to convert to SWG once I get the pool clean.
Thanks for your help.
 
MPS is an oxidizer that is often used by those who have indoor pools. It will oxidize but not sanitize like normal chlorine does. It isn't going to hurt anything other than your pocketbook and it does show up as CC on test results. You don't need it. All you need are accurate test results, bleach, and patience.

The term "chlorine lock" originated in pool stores. There really isn't sucjh a thing as chlorine lock, per se. When pool store employees mention it, they do so usually because someone's CYA is very high, too high to effectively run a pool with, and the pool owner needs to change out water by draining to lower it. If your CYA is truly 10, this is not your problem at all. Rather, your CYA being 10, you cannot keep FC in your pool because number 1, your are losing all a bunch of FC to the sunlight which burns it off really quickly, and two, you have algae in your water and that is consuming your FC as well. So, if your CYA is 10, it needs to be raised a bit so your FC won't deplete due to sunlight.

What you need first off is your own service type test kit. You aren't going to find one at the pool store. The only way to get one usually is online. You need a test kit with a FAS-DPD chlorine test and not a simple DPD test. You need to be able to accurately measure FC, CC, pH, CH, CYA, and TA. By going to www.tftestkits.net, you can purchase a test kit that fits these requirements. The TF-100 is the best one. Then, you can start testing your own water and get your pool squared away.
 
A couple of follow up points:

1, the reading of 10 ppm for your CYA should be suspect, the best test for CYA is only accurate between levels of about 20 - 100, trying to read above or below this range introduces a great deal of error, so even if the test was done right it may be 10, or 5 or even 15 ppm.

2, MPS can show up as CC on the FAS-DPD chlorine test for several days, there is a special test kit if you plan to use it, but in general you can assume it will all be gone in a few days.

Consider this a lesson learned, at least the pool store did not sell you something bad that is impossible to remove without draining your water. If you don't have one you really should get your own quality test kit like the TF-100 or the Taylor K-2006.
 
I have been reading this forum for some time now and I am always skeptical when they give me advice at the pool stores. However, this morning, the pool water is clear, one day after "shocking" with the MPS. I will check the chlorine level when I get home later today.
 
MPS is a tool and has a place, but that place is rarely if ever needed in a typical residential outdoor pool, also remember MPS is only an oxidizer, and not a sanitizer (it does have some sanitizing properties, but they are too slow for it to be considered a sanitizer on its own at pool water swim temperatures). In the above case the MPS probably provided just that little bit of extra boost to get over the final hump also the cal-hypo being used may have been contributing to the cloudy water (this is part of the reason we generally suggest avoiding cal-hypo, particulalry so while trying to clear a pool), chances are the same thing would have been accomplished with just a little more bleach and time at a much lower price.

Places where MPS may be useful include indoor pools, hot tubs, and high use and high temperature pools, such as small therapy pools, about the only time I would consider its use in typical residential outdoor pool would be if you plan on having multiple large swim parties on back to back days, even then I would caution its use without using the special MPS test to counteract it being read as CC on the conventional chlorine tests.

Ike
 
Thanks. I purchased 2.5 pounds of MPS for the spa. I later found out that it adds a lot of salt to the water. So use in my hot tub is not recommended. I will use in pool after large parties....just wanted to know what MPS was going to do to the water chemistry. Thanks.
 
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