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Thread: Two Questions: 1. On Yellow Muriatic Acid 2. On Phosphate

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    Join Date
    Aug 2008
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    Honolulu
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    Two Questions: 1. On Yellow Muriatic Acid 2. On Phosphate

    I recently purchased some Muriatic acid and it was yellow in color I noticed it took one and a half times the normal measure to reduce the pH by the same amount versus the clear Muriatic acid I normally get, the manufacturer was the same.

    At the hardware store I normally purchase the acid from I did notice the container was dusty, on asking the assistant manager he stated that since home construction was slow in Hawaii they have been selling less. In addition I always unscrew the cap to make sure it has never been opened and I did notice the normall shiny stainless steel caping over the clear plastic cap looked mottled. Next time I will be more picky. I normally feed acid automatically but the pump is broken and the new one has yet to be installed.

    On looking this up on the internet I found comments that the acid had oxidised, I am not sure if this is the case or not. Would this change in color, other than needing more to do the same job, cause any other issues such as staining? I think not but I just wanted to be sure.

    The second question concerns my friend's pool who keeps his pool at about 8 ppm Chlorine (to avoid Mustard algae), 32 to 35 CyA, 575 ppm Ca, 70 ppm Alk, salt at at 3200 ppm, and a pH of 7.4 ppm. The question is that the phosphate reading is 3500 ppm approximately, if I remember reading somewhere on the net correctly (and I am probably wrong) that high chlorine readings can lead to false phosphate readings, yes or no? If this is so would it be better to dilute by adding 2 parts tap water to one part pool water so the chlorine reading is approximately 2.67, and then multiply the phosphate reading by three?

    Any help would be appreciated.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    Re: Two Questions: 1. On Yellow Muriatic Acid 2. On Phosphate

    Muriatic acid comes in many different strengths/concentrations. Was the bottle labeled as being the same strength as you have been using before? Muriatic acid can be yellow sometimes. That doesn't really affect anything or mean anything. It has an extremely long shelf life.

    Why do you care about the phosphate level? Just ignore the phosphate level. Most of the phosphate tests are not significantly sensitive to the FC level, but you could try dilution if you want. High FC levels result in false high PH readings, which is probably what you were thinking of.

    Mustard algae can be very difficult to kill. Once you do kill it all, there is no longer any need to maintain higher than usual FC levels.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Two Questions: 1. On Yellow Muriatic Acid 2. On Phosphate

    JasonLion,

    Thank you for the quick reply.

    Yes both the Muriatic acids were both 31.45%, I just checked the old empty plastic jug. From what you wrote I assume that this yellowing is not an issue other than my need to add 1.5 times the normal amount. I will just check the caps next time. Unfortunately as nearly everything is shipped by boat to Hawaii some items can sit a very long time in hot oceanside wharehouses before they are moved to retail stores, and sadly our dock infrastucture as regards wharehousing is not state-of-the-art by any measure.

    And thank you for the info on the yellow mustard gas I will pass it on and let him know that he can lower his chlorine level.

    Aloha.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

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    JesseJames's Avatar
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    Sep 2009
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    Florida
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    64

    Re: Two Questions: 1. On Yellow Muriatic Acid 2. On Phosphate

    I noticed my last two bottles of muriatic acid did not have the tin-foiled seal under the cap. It made me think the store may have been buying it in larger containers and refilling old bottles. I used it anyway.
    13K Gal., Plaster, SWG, Intellichlor IC 20, Sta-Rite 1 HP Pump, Sta-Rite PLM 300 Filter, Pentair LED, Solar, Screened Enclosure, Great White, TF-100

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