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Thread: Low TA and ALK adjusted to normal levels lead to blue pool

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    Low TA and ALK adjusted to normal levels lead to blue pool

    Ok so.....this is where i'm at. A customer called us a week ago to close a pool. I checked the levels in the pool and the PH was below 6, ALK was 0. They had been using HTH trichlor tabs for at least this season. Also i'm pretty sure they never adjusted PH.....or checked it. So over the last week I raised the ALK to 100 PH to 7.6. Now upon returning to the pool over the weekend the water has turned blue and blue flecks are precipitating out of the water. This is to the point it will stain....if I dont let it collect in the filter. ......now I have seen this once before, after being called when the pool turned blue. Now both of these have 2 things in common, they both used HTH and they both had thier PH adjusted drastically over a few days (using soda ash, and sodium bicarb for ALK). Does anyone have any experience with this? I believe it is a chemical reaction between the PH and the clarifier that's included in the HTH.
    24' round above ground, 13500 gallons, vinyl liner, 18" Sand Filter

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    y_not's Avatar
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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    GOSH!!! One more reason to stay the hay away from Walnasty!!

    Could it be the copper that is in those tablets? I know copper goes green, not blue in the presence of CL. But is it possible for it to go blue against maybe a blue liner or pool surface?
    Highly, highly oxidized copper out in the elements is almost blue in the right, low Kelvin lighting. That green + almost blue hue really leans more toward the blue hue.
    Say at dawn with an overcast sky possibly.

    Lastly, copper sulfate is a ROCKIN' blue!

    PS. Do you have a picture? Pretty please??
    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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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    It's probably copper. What more can you tell us about the pool?

    How were the tabs added (skimmer, feeder etc)?

    Is there a heater?

    What material is the pool (vinyl, fiberglass, plaster etc)?

    What are the calcium and the cyanuric acid levels?

    Can you test for copper?

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    http://s1356.photobucket.com/albums/q72 ... oolandspa/

    There ia a link to some pics...(I can't figure out how to post directly.)

    It is a vynil lined pool, only a couple of years old,and it has a heater.

    CAL 300
    CYA 50
    24' round above ground, 13500 gallons, vinyl liner, 18" Sand Filter

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    Quote Originally Posted by PJ
    http://s1356.photobucket.com/albums/q728/pruettspoolandspa/

    There ia a link to some pics...(I can't figure out how to post directly.)

    It is a vynil lined pool, only a couple of years old,and it has a heater.

    CAL 300
    CYA 50
    I suspect the precipitation is from the heater.
    Will it brush loose and vacuum out to waste?
    I would suggest adding a sequestrant, for insurance.
    In the future, whenever trying to bring a pool back from a low pH, low alkalinity condition, add a sequestrant and leave the pool running 24/7.
    In the industry, CSP (Certified Service Professional) by the NSPI and it's successor the APSP. My company services over 600 pools every year. I think the practices regularly espoused on this forum (especially the BBB method) are outstanding; however my comments will be often oriented towards the goal of getting it done, and getting it done right now!

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    Yes it does come loose and vacuum to waste. The filter is getting most of it. Why did it all of the sudden turn blue when we got it balanced and not before?
    24' round above ground, 13500 gallons, vinyl liner, 18" Sand Filter

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    Quote Originally Posted by PJ
    Yes it does come loose and vacuum to waste. The filter is getting most of it. Why did it all of the sudden turn blue when we got it balanced and not before?
    My guess is that there's a huge amount of copper in the water (you'll probably be selling them a new heater soon). I suspect that the water is pretty hard (high calcium hardness). When you aggressively increased the pH and alkalinity the result was a solid precipitate. I would like to see some other comments on this.
    In the industry, CSP (Certified Service Professional) by the NSPI and it's successor the APSP. My company services over 600 pools every year. I think the practices regularly espoused on this forum (especially the BBB method) are outstanding; however my comments will be often oriented towards the goal of getting it done, and getting it done right now!

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    I guess what I will do is get most of it out and put in a sequestering agent for the winter just to be safe.
    24' round above ground, 13500 gallons, vinyl liner, 18" Sand Filter

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    See copper carbonate which is a blue-green color and would form from a high TA and pH combination since that increases carbonate levels substantially. See copper hydroxide as well and is pale blue though this forms from high pH independent of the TA level. It's copper oxide that is darker.
    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: Low TA and ALK adjusted to normal levels lead to blue po

    In the future, I would recommend that you avoid using sodium carbonate and only use sodium bicarbonate to recover from a zero TA situation, especially when copper is suspected to be in the water.

    Also, do you know why the CYA is only 50 ppm if they have been using primarily tabs for at least a full season?

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    Quote Originally Posted by JamesW
    In the future, I would recommend that you avoid using sodium carbonate and only use sodium bicarbonate to recover from a zero TA situation, especially when copper is suspected to be in the water.
    Why would you use baking soda to correct a low TA & PH problem? True it raises both pH and TA, but the latter to a much lesser extent. So since he was starting with zero for TA, to get up to the minimum of 90, he would have to horribly overshoot pH to get there. Then it would have to be followed up with MA and quite likely aeration to bring pH back up. That is depending on how far you'd have to overshoot the TA to compensate for the whole mess.

    Sounds like an absolute nightmarish endeavour that I would not wish to undertake.

    I would have done exactly what he did with adjusting things with both chems.

    Chemically I just can't fathom a reason as to why using bicarbonate solely, would prevent the precipitation of the copper. Also, it turned blue because it oxidized in the presence of CL, which I would think bringing the TA and pH inline allowed the CL to oxidize the copper once it came out of solution.

    But I'm no Chem Geek.
    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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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    The issue with using pH Up is that it can overshoot the TA if you use it for adjusting pH. Whether this happens or not depends on how much carbon dioxide outgassing has occurred. However, using baking soda to adjust the TA then has the pH be too low even though it does raise the pH some. Usually what is required, if only using these two chemicals, is to use pH Up to adjust for the pH and TA together but stopping when it hits the TA which it should do first, and then aerating the water to get the pH up the rest of the way. Instead of aerating, one could use a pure base at this point where 20 Mule Team Borax is reasonably close (lye would be more pure), but if one goes this route then one should stop before the TA target because adding a base will raise both pH and TA (though raises TA half as much as pH Up).

    Another approach would be to use a pure base (lye) to raise the pH and TA until one gets close to the pH target and then use sodium bicarbonate (baking soda) to raise mostly the TA the rest of the way. This is the technically cleanest way to do this, but it would require a pure base which we don't normally use in pools (i.e. lye).

    As for metals in the water, it's more important to just raise the pH and TA slowly. Then again, one might consider precipitating in the water as a good thing since this can get filtered out and is a way of removing the copper. The problem is if this precipitation results in staining of pool surfaces.
    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: Low TA and ALK adjusted to normal levels lead to blue po

    So the copper level in the pool was 1.7 after I put a sequestering agent in. Now I am going to do a partial drain and refill.
    24' round above ground, 13500 gallons, vinyl liner, 18" Sand Filter

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    Quote Originally Posted by PJ
    So the copper level in the pool was 1.7 after I put a sequestering agent in. Now I am going to do a partial drain and refill.
    That's an insanely high level of copper. I think you should consider draining the whole pool and putting in all new water and starting over. You should also carefully inspect your customer's heater, as it has certainly been severely damaged.
    In the industry, CSP (Certified Service Professional) by the NSPI and it's successor the APSP. My company services over 600 pools every year. I think the practices regularly espoused on this forum (especially the BBB method) are outstanding; however my comments will be often oriented towards the goal of getting it done, and getting it done right now!

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    Well the customer just wants me to close as is.
    24' round above ground, 13500 gallons, vinyl liner, 18" Sand Filter

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    I have had to deal with many zero, and very negative, TA pools. I only use sodium bicarbonate, and it always works.

    The pH recovers just fine. How much bicarb moves the pH depends on where the pH starts. The lower it is, the more the pH rises. As the pH approaches 8.3, the pH rise drops off exponentially. This prevents overshooting the pH, especially locally. In fact, if the pH started at over 8.3, adding bicarb would actually lower the pH.

    The problem with using sodium carbonate is that carbonate is much more likely to cause a precipitation reaction, especially if it is added too fast and there is locally high pH.

    Bicarb combines with the excess hydrogen ions to form carbon dioxide and water. The carbon dioxide off gasses and the net effect is the same as adding a base like sodium hydroxide. There is no excess buildup of carbonate alkalinity.

    HCO3- + H+ <> CO2 +H2O

    More than half of the bicarbonate added becomes CO2 until the pH reaches about 6.35 and then the percentage decreases steadily from there.

    In most cases, the pH will be at least 7.2 by the next day after adding the correct amount of bicarbonate.

    When you use sodium carbonate, the more than half of the carbonate picks up two hydrogens to form carbon dioxide and water until the pH reaches about 6.35.

    CO32- + 2H+ <> CO2 +H2O

    Therefore, until a pH of 6.35, you're getting the same thing, only with more risk of an adverse reaction.

    As the pH passes 6.35, less than half of the carbonate ions pick up two hydrogens to form carbon dioxide and more than half of the carbonate ions pick up one hydrogen ion to form bicarbonate.

    In any case, I have successfully used bicarb only to recover from zero, and well below zero, TA pools.

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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    Below zero TA - we are not in Kansas anymore...

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    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
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    Re: Low TA and ALK adjusted to normal levels lead to blue po

    JamesW, thank you for that helpful info. I'll make a note of that information. I appreciate it.

    I do have a question or 2 about it though. But I don't have the time ATM so I'll ask you later.

    Thx.

    UWV, You dork! :P
    LOL
    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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