Purple ph test sample.

Problems relating to pH and total alkalinity. Increase ph, increase TA. Reduce pH, reduce TA. pH chemistry advice and techniques.

Purple ph test sample.

Postby Moose » Wed 14 May, 2008 12:16

New SPA owner.


I have a K-2005 Taylor test kit. When testing my ph level, I fill my comparator tube with 44 ml of test water and add 5 drops of R-0004 ph indicator solution. I then cap the tube and invert it. The red colour immediately changes to a rich purple.

Does this indicate a very high ph level? I have tried the acid demand test a few times. Adding drops of R-0005 acid demand will change the test water to a clear colour after 30 or so drops.

The total alkalinity is 120 ppm. Bromine is 5 ppm. Temperature is 100F. Water is crystal clear.

Thanks for any help you may be able to offer.
Moose
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Postby chem geek » Wed 14 May, 2008 16:44

Yes, purple means high pH as shown here. However, when you added drops from the acid demand test and invert to mix, then the color should have changed to the lower colors on the tube -- towards orange and then yellow. Did it do that and then turned to clear when you added a lot of drops? The idea isn't to turn clear, but to see how many drops it takes to get to the orange-red color that is around 7.5
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Postby Moose » Thu 15 May, 2008 08:25

Thanks Chem Geek

I just finished my daily ph test.

Adding drops during an acid demand test, I went further than the "clear" water colour. I found that as I got over 50 drops, the colour started to turn yellow and I would assume on to orange if I had had more R-0005, but alas, I have used up my supply. I will pick up some more today.

The SPA is approximately 1000 gallons. I intend to add a few ounces of acid daily, till I get things in order.

Does this sound like the correct thing to do?

Thanks again.
Moose
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Postby chem geek » Thu 15 May, 2008 10:28

Wow. If that's true, then the pH must be through the roof, but that doesn't sound right unless you added a chemical to raise the pH. Did you ever add a Spa Up product?

As for getting to yellow in the pH test, that would be low pH. What concerns me is that you got it to turn clear which is not normal. So I'm not so sure I trust this pH test.

You can do a simple bucket test before tinkering with your spa. Just take a bucket of spa water and add a small amount of dry acid to it -- say 1/4 teaspoon. Then see what happens with the pH. I'd also consider getting another pH test or having a pool/spa store test your water (take a sample to them).

Richard
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Postby Moose » Thu 15 May, 2008 13:56

Thanks Richard

I tried your "simple bucket test". Very clear now that my ph is sky high.

Can you give me an idea of how fast I can add acid? The SPA holds around 1000 US gallons.

p.s. - I had not added anything other than bromine tablets to the municipal treated water that I had trucked in a week ago.

Dave
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Postby chem geek » Thu 15 May, 2008 15:10

Wow. I don't understand how your pH got so high in the first place. I doubt the municipal water was much over 8.0 in pH and if the TA were really high, then that can account for a further rise in pH from aerating jets, but your TA is at 120 ppm which is on the high side, but not extraordinary (especially when using bromine tabs which should be a little acidic).

I suggest not going to far overboard with the acid. Let's assume that your TA number of 120 ppm is correct and let's assume that your pH is around 8.5. Then adding 4 fluid ounces volume of dry acid (that's 8 tablespoons) should lower the pH to 7.2 in 1000 gallons. You can then allow this to mix for at least 5 minutes with the circulation pump (not aeration jets) running and then retest the pH. If the pH is still off the charts (purple beyond 8.0), then add another 4 fluid ounces, wait, and retest. It should be in the measurable range at that point and then finer adjustments can be made.

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Purple ph test sample.

Postby RK » Wed 05 Jan, 2011 10:35

I was consulting with Ecolab on this same issue and they said the purple color could mean a variety of things:
1) high pH
2) old reagent
3) reagent too cold and will not act proper

Hope that helps.
RK
 

Purple ph test sample.

Postby Pool User » Thu 14 Apr, 2011 14:04

The reason for the purple in the sample is because the test kit is designed to give you a false reading if the clorine or bromine level is extremely elevated like over 10ppm Check the clorine or bromine level first and then re test your PH. I bet that you will find the the clorine/bromine level is very high.
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Purple ph test sample.

Postby chem geek » Thu 14 Apr, 2011 20:25

This is an old thread, but yes a high chlorine level, usually above 10 ppm Free Chlorine (FC), can cause a false high pH reading that looks purple. The quote from Taylor's Pool & Spa Water Chemistry booklet on the issue of a high FC causing a false high pH reading is as follows:

FALSE READINGS: high levels of chlorine (usually > 10 ppm) will quickly and completely convert phenol red into another pH indicator (chlorphenol red). This new indicator is a dark purple when the water's pH is above 6.6. Unfortunately, some pool operators mistake the purple color for dark red and think the pool water is very alkaline and wrongly add acid to the pool.

When a sanitizer level is not extreme, only some of the phenol red may convert to chlorphenol red. However, purple + orange (for example, pH 7.4) = red. This error is more subtle as no purple color is observed and the operator does not suspect that a false high pH reading has been produced. Some operators neutralize the sanitizer first by adding a drop of chlorine neutralizer (i.e. sodium thiosulfate). However, thiosulfate solutions have a high pH and, if heavily used, may cause a false higher sample pH.
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Purple ph test sample.

Postby Don't put acid in yet » Sat 16 Jul, 2011 11:21

If your chlorine is high the test will read purple regardless of ph. I am been adding acid like a dope for two weeks. If you don't have sodium thiosulfate, just run the pool water through a drinking water activated charcoal filter, like the britta one in your fridge, and retest, my so called over 8 ph was really less the 7.2.
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