Free vs. Combined Cl

[Bill_Stevenson]

For the past month or so I have been taking a sample of the water to a local pool & spa supply place for testing.  This store is very convenient to my house and the merchant has been in business for many years and came highly recommended.  They sell Bio Guard products.  Anyway, they have been telling me what chemicals to add to my water and all seemed OK until this past Saturday.  On Saturday the total Cl came in at 10-ppm, and the free Cl came in at 8.5-ppm.  The computer read out said that I should add 3-Tbs plus 1-tsp of  Cl as a shock!  I asked, why would I add any Cl until the value went back down to 3-5-ppm?  Answer is that it is because of the combined Cl value being above the free Cl concentration.  It was suggested that I might shock with MPS instead.    

I decided to wait another day and then see.  Total Cl fell to 3-ppm (using test strips - that is a different measurement technique), therefore, I did shock last night after my soak.   The spa had been shocked last Sunday (i.e. 7 days prior) and used only twice by one person during the week.  After each use, 1-tsp of Cl was added.  Frankly, I was surprised that total Cl was so high, but I had been away all week and did not test at all in consequence.

Does all this sound reasonable?  Should I just shock as per the computer read out even if Cl concentrations are this high?  Should I consider shocking with MPS if this happens again ?  

Thanks,

Bill    

[Vinny]

Bill,

The reason for that much chlorine to shock is to get the free chlorine to 7 to 10 times the amount of combined chlorine to break the combined chlorine concentration. But with 8.5 PPM you would only need another 2.5 to 6.5 PPM added to the 8.5 PPM already there.

Be aware that some pool people don't trust the accuracy of the computer readers due to possible calibration errors.

Can you get a hold of a Taylor K-2005 kit. These are extremely accurate and you're not at the mercy of a possible wrongly calibrated computer.

If you want or need more info, just ask and I'll try to answer.

Vinny

[Bill_Stevenson]

I know these people calibrate their computer reader daily, and they have re-calibrated it right in front of me on one earlier occassion.  They did say that calibrating the computer reader is both tricky and necessary.  They also mentioned the Taylor test kit to me, and they use one too, if there is any question.  They sell the Taylor kit, but only on special order so as to get fresh chems.  

In discussing testing options, they showed me the kit and ran tests with it on my water to demostrate and also to verify the computer reader.  My impression was that the colors in the Taylor kit are difficult for my eyes to see.  I am not color blind, but had trouble differentiating the slight color variations that the liquids were displaying.  Other people seemed to have less trouble reading the results, so this is apparently a weakness in my eyes.  That is why I decided upon the weekly run to the store with a sample.
It was not lost on me that they test for free and make a few bucks if I bought a Taylor kit.  Of course they appreciate my business and seem genuinely interested in providing both good service and advice to me as a customer.

My question remains, should I switch to MPS for shock?

Regards,

Bill

[Vinny]

I haven't used MPS in my pool (no tub yet) but from what I've read on this and Doc's board you probably can use MPS and this way it'll break the combined chlorine and won't raise your chlorine level.

[Bubbles]

Simplify your life Bill. Seems you are working way too hard on this. Test free chl (1-5ppm) and shock once a week. Don't micromanage your water. Might seem cool now but this love afair won't last.

[Bill_Stevenson]

Well I don't want to get into an argument, but what did I say that indicated that I am micromanaging my water?  What did I say that would lead to the conclusion that I don't shock once a week?  Why can't I get a simple answer to a my question?  Does anybody have any experience with MPS?

Thanks,

Bill

[wmccall]

I use the MPS to shock with about once every 2 weeks.  Or if by neglect the water gets cloudy. It seems to me MPS bring cloudy water back to clear faster.  The knock on MPS is that it adds to TDS, but using it about once every two weeks I still get 3 months out of water. I think one way to alleviate the TDS issue is to use unbufered MPS.  Some products are buffered to prevent it from changing the PH. I think I remember that pure MPS tends to raise the PH level. I'm usually on the low end of PH anyway. I bought some non buffered MPS from Doc.

[Bubbles]

Well I don't want to get into an argument, but what did I say that indicated that I am micromanaging my water?  What did I say that would lead to the conclusion that I don't shock once a week?  Why can't I get a simple answer to a my question?  Does anybody have any experience with MPS?

Thanks,

Bill

No argument, just offering an opinion. Seems that you are all hung up on fr/ttl chlorine. That was the indication that lead me to believe so. As my prior post stated; test free chl and shock weekly. You are very welcome Bill. Micromanage away!

[windsurfdog]

I think I remember that pure MPS tends to raise the PH level. I'm usually on the low end of PH anyway. I bought some non buffered MPS from Doc.

Terminator,
I use unbuffered MPS as well.  I believe it has a pH of between 3-4 so it should cause your pH to drop.  Coupled with testing and correction with either soda ash or baking soda (depending on whether TA is good or low) is the tack I take.  Let me know if you find anything different with what I believe is correct....works for me anyway.

[Soakin]

If you haven't already seen it, the Vermonter discussion of chlorination on Doc's site may be helpful.  Although the author prefers chlorine shocks, the posting does address MPS, describing situations where it is appropriate.    

http://www.rhtubs.com/dichlor_vermonter.htm

The short version:  In the situation you described (High total and free chlorine) MPS makes sense.  I would think that the concerns mentioned previously regarding TDS and pH drift would not be an issue with occasional use.  (By the way, I think the pH will tend to go down with MPS, not up)

One thing to think about:  How did the chlorine levels get so high?  Did the person using the tub while you were gone perhaps confuse tea and tablespoons?  Another possibility:  are you shocking at the rate of 3 T plus 1 t?  If you are regularly dosing 1tsp, a rate of 2T plus 1t would be more in line with the Vermonter recs.  

p.s.  Your posts indicated that you went ahead and shocked (I am assuming with dichlor) after the levels came down.  What happened to your test results after that?

p.p.s.  For what it is worth, I don't think trying to determine which chemical tool is most appropriate in your situation is "micromanaging".

 

[Bill_Stevenson]

Thanks to all for your comments.  I really appreciate it.  For the record, I do use the Vermonter's regimen and had not run into this problem before.  It is possible that while I was away the fellow who took care of it did mistake tablespoons and teaspoons.  I will ask him, as that is a good thought.

I would prefer not to use MPS, but based on the information provided here, I will try it if this situation occurs again.  

As for the amount of dichlor used to shock, the 3-Tbs plus 1-tsp was what the computer readout recommended.  In the past I have shocked using 2-Tbs.

Regards,

Bill

[wmccall]

Terminator,
I use unbuffered MPS as well.  I believe it has a pH of between 3-4 so it should cause your pH to drop.  Coupled with testing and correction with either soda ash or baking soda (depending on whether TA is good or low) is the tack I take.  Let me know if you find anything different with what I believe is correct....works for me anyway.

I stand correct, not that it is unusual, or that I am thinking clearly today. Perhaps its Bromine that has a natural PH of 8.   Like the more clear thinking W Surf dog, I just add a little baking soda if my ph and alk get low.

[Lori]

Another water care system to check out on the faq's at Doc's site is Northman's.  He does use MPS.  I used the MPS that came with my tub but haven't replaced it.  I continue to use just Dichlor for sanitizing and shocking.  The MPS did seem to clear the water faster, but I found, after my bottle the dealer gave me with my brand new tub, I had my maintenance down pretty pat, and didn't need the MPS anymore.

I would consider using it again if I ran into problems!

[Guttboy]

OMG!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


You guys are making my head spin!!!!


Is it really that hard to maintain the water quality of a Spa?

Regards,

Mike

PS...this is not a sarcastic question....it is 100% serious.

[Lori]

No, Guttboy, it is not that hard to maintain your water!

There is a learning curve for newbies.  For me it was a few months of constantly testing (with a Taylor Kit) my water for levels.  I would test everything, free chlorine, combined chlorine, total chlorine, ph, and alk.  I would do this every other day.  I wrote down all of my measurements in a calendar, so I could track what my water was doing.  Yes, I know I am anal about things.  What I learned was my water doesn't change drastically, but gradually over time.  After about a month of fresh water, my ph and alk drift down, so I add a little baking soda to raise them.  Other than putting in chlorine when I am finished soaking and shocking with chlorine once a week, that is all I do.

How much easier could it be?  But that is my local water.