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Thread: PH test shows purple

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    PH test shows purple

    I was starting to get my pool ready to close yesterday when I thought I'd check the light niche for algae. When I pulled the light out the niche belched out this gray brown cloud. The niche was full of this stuff. It was impossible to capture any of it as it just disolved when I tried to collect it. I've got the clorine up to 20 and I dumped in some algecide as well. When we measured the chemistry this morning the ph is off the charts. We are using the Taylor Basic kit that comes with the TF-100 kit. Using the pool calculator we entered 8.2 (highest reading on the tester) for the ph with a target of 7.2 it told us to put in 132 ounces of muratic acid. We did that about noon today. This evening I tested it again and the test originally showed 7.5 but less than a minute later it was purple. The pool became cloudy last evening but is clearer this evening. We have a 28,000 gallon, 18' X 36' inground vinyl lined pool with a S240 Hayward sand filter. We live in Wichita, KS. Should we expect to see a spike like this with introduction of such a large amount of algae? What would you recommend we do to combat this? Any help is appreciated.

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    dmanb2b's Avatar
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    Re: PH test shows purple

    The PH test will read falsely high when FC is above 10ppm. Can you post a full set of test results?
    24'x52" AGP (13,500 Gallons), Intex SWG, (2)Solar Bear 4x20 panels, Hayward S220T Filter, 1/2hp Pentair Superflo

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    Re: PH test shows purple

    My readings are as follows:
    FC 24.5, CC 1.0, ph 8.2+, , TA 160, CYA 90.

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    Re: PH test shows purple

    7.5 is probably the pH. The purple is probably due to high chlorine interference. The pH will probably be fairly accurate if read right away. However, the pH test will be most reliable when the FC is below 10 ppm. With a TA of 160, you might be at risk of scaling if your calcium is high.

    What is your calcium level?

    What is your chlorine source (SWG, bleach, tabs etc.)?

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    y_not's Avatar
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    Re: PH test shows purple

    Quote Originally Posted by Truman
    My readings are as follows:
    FC 24.5, CC 1.0, ph 8.2+, , TA 160, CYA 90.
    Your CYA is far, far too high. In fact, if CYA registers at 90 using the turbidimetric test. It is recommended to re-test it with a 50/50 dilute of the solution + tap water. The instructions are in the "Extended Test Kit Directions" thread, under the "Testing & Balancing Your Water" topic.

    If you are going to do an affordable, realistic shock. It would be advised to drain your pool by 40-50% to get your CYA levels down below 50. But only after you have verified that the test isn't higher than 90 by doing the dilute method above.
    I presume you were using pucks?
    Shock level for your CYA, according to Chem Geek's chart in "Pool School" is 35ppm FC!!!! That's a lot of bleach, it won't hurt your pool at that CYA level, just your bank account.

    Conversely, shock level at 40ppm CYA is 16ppm FC. Much easier to maintain and shock.

    I would just ignore your pH, unless you know it was high before you started. If it was, then you can add some acid, approximating from your prior reading. But the only real way to be sure on your pH, is to let the FC drop and that's not good once you start the shock process. You loose any headway you have made against the unwanted microbial guests in your pool.
    Thanks for reading... - Tony
    Da' Pool: Intex 15'x42" 3284gal AGP EasySet (Inflatable Ring) - (Summer 2014: 27' round EW /w 6.5' deep end @ 22,500gal)
    Pump & Cart Mod: 1000gph Cart. 5ft² - 2 nylons, 24/7 OP. Traps bugs/bits, lasts longer/cleans easier = Happier Pool Owner!!
    The Bible for a "Trouble Free Pool" life = PoolSchool, the BBB method a TF100 test kit(Recommend Kits Compared). - Cleaning a Sand Filter
    Water looks like GLASS, if yours doesn't...SLAM IT! Feels nice and never been happier!!! :D

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    Christian's Avatar
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    Re: PH test shows purple

    To get a more accurate pH level you can add 5 drops of #7 (chlorine neutralizer) from your tf100 kit. You want to do this before you add the pH reagent.

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    UnderWaterVanya's Avatar
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    Re: PH test shows purple

    Quote Originally Posted by Christian
    To get a more accurate pH level you can add 5 drops of #7 (chlorine neutralizer) from your tf100 kit. You want to do this before you add the pH reagent.
    I thought chem geek indicated that adding Sodium Thiosulphate could bias the test towards base also. I know it is used in some pH tests but his critique of this was that it was not the best choice. If I remember he said that adding DISTILLED water (0 FC and 0 TA) would allow you to dillute the FC and not alter the pH and then test it with lowered FC. I think the specific example was for a FC that was not above 20 so that only a 50/50 dilution was needed. I have had luck reading the test QUICKLY at FC between 11-18 but not above that.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
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    Re: PH test shows purple

    Sodium thiosulfate solutions can be high in pH themselves and their effect on pH from reacting with chlorine varies as well. This is why Taylor puts in a combination of reducing agents in their pH solution that tend to cancel each other out in terms of their effect on pH when neutralizing chlorine, at least up to 10 ppm FC or so. Reading the pH test quickly will work if the FC/CYA ratio isn't very high. Diluting with distilled (unbuffered) water will also work since that dilutes the FC level with virtually no change in pH (the buffering in the sample water keeps the pH nearly constant when mixed with unbuffered water).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: PH test shows purple

    Thanks to everyone for all of the great information. I tested the water this evening and here are my results. FC 24.5, CC 1.0, TA 130, PH 7.2-7.5, Calcium 310. It has held that chlorine level for two days. We use bleach as our chlorine source.

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    y_not's Avatar
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    Re: PH test shows purple

    What is your CYA level at, did you do a 50/50 dilute test?
    If it's still 90, shock level for that is 35ppm FC, you're too low. This is why you do a partial drain to lower CYA. It's just expensive to shock.

    Also, you aren't finished shocking until you pass all 3 criteria listed in Pool School.

    1. CC is 0.5 or lower;
    2. An overnight FC loss test shows a loss of 1.0 ppm or less;
    3. And the water is clear.

    An OCLT is done after sundown when dark, then before sun up, preferably before dawn or around dawn. No direct light on the pool.
    Thanks for reading... - Tony
    Da' Pool: Intex 15'x42" 3284gal AGP EasySet (Inflatable Ring) - (Summer 2014: 27' round EW /w 6.5' deep end @ 22,500gal)
    Pump & Cart Mod: 1000gph Cart. 5ft² - 2 nylons, 24/7 OP. Traps bugs/bits, lasts longer/cleans easier = Happier Pool Owner!!
    The Bible for a "Trouble Free Pool" life = PoolSchool, the BBB method a TF100 test kit(Recommend Kits Compared). - Cleaning a Sand Filter
    Water looks like GLASS, if yours doesn't...SLAM IT! Feels nice and never been happier!!! :D

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