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Thread: pH rise in spa that was just drained & refilled

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    pH rise in spa that was just drained & refilled

    New here and this is my first post. In fact I'm new to the whole pool/spa maintenance thing, but I just completed the CPO class. I have a 1,000 gallon hot tub, which is using hydrogen peroxide and U/V light to sanitize.

    I cannot get the pH to come down and stay down at a reasonable level. In fact I cannot get it down even to 8.2. If I drain the tub and refill, which I have done twice in a month, the pH of the new water starts at 7.4/7.5.
    Here are the values I measured just after filling the spa:
    TA: 100
    Hardness: 220
    H2O2: 0
    pH: 7.5

    I turned on the heater and the circulator pumps, left it for 24 hours, and the pH has risen off the chart. Other than temperature (95 degrees,) the other numbers have not changed.

    What is causing this, and what do I need to do to keep the pH down?
    I'm beyond measuring for the "correct" amount of chemical to add. I've added up to 8oz. of muriatic acid at a time, no help, and one pound of sodium bisulfate. No change.
    10,000 gal inground
    Pac Fab Challenger 1hp pump
    StaRite cartridge filter

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    Re: pH rise in spa that was just drained & refilled

    Hydrogen peroxide is alkaline upon usage and will account for some of the pH rise.

    [edit]It depends on what the hydrogen peroxide is oxidizing. If it's something like ammonia, then it will end up being more pH neutral.[end edit]

    The other source of pH rise is the TA. Keep adding acid until the pH and TA go down and stay down. The TA will probably need to drop to about 40 to 60. As long as you're using 31.45 % acid, the pH and TA will go down. If the pH and TA won't go down, then there is something wrong with the acid. Do not lower the pH to less than 7.2.

    It's also likely that you have some scale built up. Some of the acid will be used up dissolving the scale until the scale is mostly dissolved.

    Is the spa plaster, tile, fiberglass or what?

    Is the surface smooth or rough with scale?

    I'm guessing that you're probably in South Australia where hydrogen peroxide + UV is approved for commercial use?

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    Re: pH rise in spa that was just drained & refilled

    It's a fiberglass tub. The surface is smooth and not rough with scale. There is no hydrogen peroxide in the tub as I just drained it. Nothing but tap water, which was 7.5 when it went in yesterday and jumped to 8.2+ overnight with nothing but the heater and the jets. The spa is outdoors though, in the sun.
    I'll start dumping acid in there today, keep the pool closed for the week, see if I can get the numbers down. I thought TA was supposed to be 80-120 though?
    And South Australia? No, I'm in Colorado.
    10,000 gal inground
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    Re: pH rise in spa that was just drained & refilled

    I didn't know hydrogen peroxide + UV was approved in the US for use as a primary sanitizer. The TA does not need to be 80 to 120 ppm; it can be as low as necessary to maintain the pH.

    There is no need to keep the pool closed for a week. With hot water and good circulation, it won't take very long to get the TA down. Add the muriatic acid and then recheck the pH in 10 minutes.

    Keep lowering the pH to 7.2 until the TA gets down to about 60 and then only lower it to about 7.6 until the it stops rising.

    When you're reporting Hardness as 220, is that Total Hardness or Calcium Hardness?

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    Richard320's Avatar
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    Re: pH rise in spa that was just drained & refilled

    I'd expect that. Tap water has a lot of CO2 dissolved in it as Carbonic Acid; same stuff that gives CocaCola its fizz. Spas get a lot of aeration, which drives out the CO2, lowering the acidity, and making the pH go up.

    Keep adjusting pH as it rises; eventually your spa will hit the sweet spot where it all holds fairly stable. Draining and refilling it justs wastes water.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Re: pH rise in spa that was just drained & refilled

    Quote Originally Posted by JamesW
    I didn't know hydrogen peroxide + UV was approved in the US for use as a primary sanitizer.
    Just to reiterate what JW mentioned, it is not, nor do you have any way to confirm your water is sanitary.

    Agressive aeration from the spa jets and TA over 60 is causing the PH to rise.
    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 rise in spa that was just drained & refilled

    Colorado is one of 28 states whose code requires that all Pool and Spa Circulation System Components comply with NSF/ANSI Standard 50, which requires that UV be used with a residual level of an EPA registered chemical disinfectant.

    Hydrogen peroxide is an oxidizer, not an approved EPA registered disinfectant. NSF 50 requires that UV be used with not less than one ppm free chlorine or two ppm bromine.

    This Colorado pool company says that UV + H2O2 meets code, but I don't think that they're correct.

    I'm assuming that this is a commercial/public pool, is that correct? Has the health department approved your facility to use UV + hydrogen peroxide without chlorine or bromine?

    [edit]Recent NSF activity seems to indicate that they are now changing the language to indicate that UV systems are intended for use with appropriate residual levels of EPA registered disinfecting chemicals, which seems to be vague, but getting away from any sort of requirement. Colorado code is also somewhat vague as to exactly what they require.
    Other disinfecting equipment or materials may be used if they have been adequately demonstrated to the Colorado Department of Health or its authorized agents to provide a satisfactory residual effect which is easily measured or where demonstration and analysis provide assurance that results are otherwise equally effective under conditions of use as the chlorine concentration required herein, and not be dangerous to public health, create objectionable physiological effects or impart toxic properties to water.
    http://www.cdphe.state.co.us/regulation ... al1103.pdf
    Also note: UV + H2O2 is approved in South Australia only for indoor pools.
    The ultraviolet light plus hydrogen peroxide (UV+H2O2) system is approved for disinfecting indoor swimming pools up to 500,000 litres in capacity.
    http://www.health.sa.gov.au/PEHS/public ... l-oper.pdf
    [end edit]

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    Re: pH rise in spa that was just drained & refilled

    So technically we're a public pool. It belongs to our condo association, so condo owners and their guests/renters are authorized to use it. We'll go for days or a week at a time with no one in it at all. It's busiest may see 6-8 people per day.
    I don't know whether it's "legal" or not - it's been using H2O2 and U/V for probably 15 years. I just inherited the maintenance job this summer.
    The answer to someone's hardness question is, it's calcium hardness I'm reporting.
    So here we go: Per the advice in this thread, I have been dumping acid in the pool and re-checking pH for the last two days. pH started at above 8.2 (off the chart) and after adding 46 fluid oz. of acid, we're still above 8.2. Do I keep going?
    10,000 gal inground
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    Re: pH rise in spa that was just drained & refilled

    Quote Originally Posted by humpndunk
    So here we go: Per the advice in this thread, I have been dumping acid in the pool and re-checking pH for the last two days. pH started at above 8.2 (off the chart) and after adding 46 fluid oz. of acid, we're still above 8.2. Do I keep going?
    Yes, add enough acid to lower PH to 7.2 and when it get to 7.8, lower it again. Eventually when TA drops to around 50-60 the PH rise dhould slow considerably.
    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 rise in spa that was just drained & refilled

    Something does not add up. Your first post says that the tub is 1,000 gallons and that your TA was 100 ppm. 46 ounces of 31.45 % muriatic acid should lower the TA by 180 ppm, which would drop your pH well below 4.5.

    Your Volume, pH reading, TA reading and/or acid strength are wrong. What is your current TA?

    I don't know whether it's "legal" or not
    As a CPO, it's your job and responsibility to make sure that it is "legal" and safe. Have you ever applied for a health department permit to operate this tub, or been inspected by the health department?

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    Re: pH rise in spa that was just drained & refilled

    Note this paper comparing sodium hypochorite vs. hydrogen peroxide. Notwithstanding the limited Australian approval, it is not approved by the EPA as a disinfectant for use in commercial/public pools.
    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
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    Re: pH rise in spa that was just drained & refilled

    According to the Colorado code, this hot tub might not be considered as public, semi-public or commercial.
    11. "Private Pool" means any pool which is constructed in connection with or appurtenant to single family dwellings, condominiums or apartment houses, and which is used solely by the persons maintaining their residence within such. http://www.cdphe.state.co.us/regulation ... al1103.pdf
    Therefore, if only the residents use the pool, then it might not be considered public. Whether or not the residents are allowed to have non-resident guests accompany them to the pool might affect the classification.

    Either way, as a CPO being paid to maintain the pool, you are still responsible for making sure that the tub is safe to use.

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    Re: pH rise in spa that was just drained & refilled

    Checked this morning... TA has finally dropped from 100 to 70, and calcium hardness from 220 to 180, no change yet in pH. Added another 22oz. of acid and will check again this aft.
    10,000 gal inground
    Pac Fab Challenger 1hp pump
    StaRite cartridge filter

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    Re: pH rise in spa that was just drained & refilled

    You should double check the volume of the tub and the strength of the acid. Something has to be off for your TA to only drop by 30 ppm after adding the amount of acid that you have.

    What else is being added to the tub?

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    Re: pH rise in spa that was just drained & refilled

    Holy ****! Everything dropped today. I think it may be because I used a different bottle of acid. I'll bet that other bottle, which I finished yesterday, had gone bad or lost strength. My pH is now down below 6.8, and TA is down to 10. Now we're getting somewhere!
    10,000 gal inground
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    dmanb2b's Avatar
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    Re: pH rise in spa that was just drained & refilled

    If TA is down to 10, your PH is dangerously low. Raise PH to at least 7.2 promptly.

    What test kit are you using?
    24'x52" AGP (13,500 Gallons), Intex SWG, (2)Solar Bear 4x20 panels, Hayward S220T Filter, 1/2hp Pentair Superflo

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