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Thread: Fighting scale and PH creep

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    Fighting scale and PH creep

    My salt water gunite pool is 30k gallons with a above level spa which has two waterfalls into the pool. I have been fighting scale and ph creep all summer. The deck and the spa are finished with stacked stone and mortar. The scale forms ontop of the stacked stone and along the walls of the above ground spa where the fountain of water falls into the pool. All other pool metrics are within normal range. I'm using muratic acid to combat both the ph creep and scale.

    Is this normal? Is the calcium found naturally in the stone contributing to my scale problem. Is there anything I can do besides use muriatic acid? The temp of the pool is typically low to upper 80s from early May until early Oct.

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    Mod Squad jblizzle's Avatar
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    Re: Fighting scale and PH creep

    Welcome to TFP!!!

    Any aeration will contribute to the pH rising ... sounds like you have a lot of it with the 2 waterfalls and the SWG. High TA can also contribute to the pH rising faster. You need to add acid as often as required to keep the pool in balance. If you let the pH get too high, calcium scaling can occur. BUT, what you are describing is not really calcium scaling I don't think. You are just seeing the deposits left behind as the water is constantly evaporating off the rocks. There is not much you can do about that.

    Please post up a full set of test results add your pool details to your signature as described HERE as it will help us help you.
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    Fighting scale and PH creep

    Please add your pool details and equipment to your signature. It will help us out a lot.

    Calcium scale is always a major problem with plaster pool that have lots of aeration. One reason to post water test results is that you can plug those numbers into the PoolMath calculator and get an automatic calculation of your Calcite Saturation Index (CSI). The CSI tells you how balanced your pool water is. Negative values lower than -0.3 indicate potential Ca etching from the plaster and pool surfaces while a positive value larger than +0.3 indicates possible scaling (precipitation) of Ca from you water.

    Once you understand your CSI value you can take steps to keep you water balanced by either adjusting pH with acid or adjusting your TA. pH, calcium hardness and total alkalinity are major drivers of your CSI values.

    pH drift in plaster pools is normally to more alkaline values (pH increases over time). For new pools, pH drift can be quite dramatic with the need to add acid almost everyday or every other day. There are ways to control pH drift by adding automatic acid dosing systems to your equipment pad and/or adding borates to your water to help slow pH rises. However, those two things should only be attempted once you have good control and knowledge of your pool waters behavior.

    Your first step is reading up in PoolSchool as much as you can focusing on The ABCs Of Water Chemistry and how to balance and test your water. Your second step is getting a good test kit (Taylor K-2006), learning how to use it and posting your test results. Finally, ask lots of questions and we'll do our very best to help you.

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    Re: Fighting scale and PH creep

    I learned quickly that I needed a good pool kit and purchased a Taylor Service Complete Pool Water Test Kit K-2006C. I have a Hayward AquaRite Electronic Chlorinator AQR15 for a pool up to 40k gallons. My pool filter is a Nautilus FNS 60.

    PH is 7.4
    FC 8.0 ppm
    CC 0 ppm
    TA = 80ppm
    Calcium Hardness 230
    CA 65

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    Mod Squad jblizzle's Avatar
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    Re: Fighting scale and PH creep

    That low CH level would require the pH to be VERY high for you to actually get calcium scaling which would show up in the pool and not just where water flows and evaporates.
    Jason, TFP Moderator
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    Fighting scale and PH creep

    Your CSI (assuming a salt level of 3500) = -0.53

    That is a really REALLY negative CSI value. That means you are potentially etching Ca out of your plaster and calcite materials in the pool (grout, stone, etc). You could be etching Ca into solution and then, as the water splashes out into surfaces, you getting evaporites deposited everywhere.

    You need to bring your pH and alkalinity up a bit. How much acid are you adding on a daily basis??

    Raising or maintaining your pH at 7.6 and increasing your TA to 100ppm would bring your CSI up to -0.25 which would be a lot better.


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    Re: Fighting scale and PH creep

    Recently I have been adding 1 quart of Muriatic acid a week. Thanks so much! Will try it to increase the TA and watch the PH at 7.6. I had a service which wasn't maintaining new pool properly. That's when I took over. It was their negligence that caused my pool to scale. They weren't adding salt to my pool! I don't even think they were testing the PH level.

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    Fighting scale and PH creep

    Quote Originally Posted by Live4Color View Post
    Recently I have been adding 1 quart of Muriatic acid a week. Thanks so much! Will try it to increase the TA and watch the PH at 7.6. I had a service which wasn't maintaining new pool properly. That's when I took over. It was their negligence that caused my pool to scale. They weren't adding salt to my pool! I don't even think they were testing the PH level.
    Well, I'm glad to read that you want to take care of your own pool. Once you learn the TFPC Method, your pool (and wallet) will be much better off!

    Adding acid and running all those waterfalls/spillways is what is lowering your TA. You may not have to add anything to your pool (aside from acid) if you can adjust the amount of aeration your water is getting. Depending on your fill water your TA could just naturally increase on it's own.

    Please describe to us what your daily and weekly pool routine is like and what features are running on your pool.

    Use PoolMath and you can do your own CSI calculations. It's a very handy tool and it lets you vary each parameter to see it's effect on your water chemistry. The bottom of the page has a What-If calculator (what happens if I add XXX oz of YYY chemical...)

    As to your comment about salt, once you establish the concentration of salt appropriate for your SWG, you should not ever have to add salt on any regular basis. Salt level only decreases through water loss, either from backwashing your filter or through heavy splash out.

    Since you say your service did a bad job and you're new to pool care, I would highly recommend the following -

    1. Read through as much of PoolSchool as you can, focusing on pool water chemistry and chemicals;

    2. Make sure you have proper water testing equipment on hand. Since you have an SWG you should have a way to test your salt levels. You can either use AquaChek Salt Test Strips or there is a Taylor drop reagent kit. Your regimen for salt testing should be a monthly basis and/or after drain & refill.

    3. Ask questions on these forums. Folks will always be willing to help. However, always be prepared to post your latest water chemistry numbers.

    4. Make sure your profile and signature are up to date with your pool specs and equipment so people helping you don't have to search for that info.



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    Re: Fighting scale and PH creep

    A TA of 80 should help prevent pH drift better than a TA of 100 though.

    Do you only run the waterfalls when they are needed? If not, it might help to do so.

    I go through a gallon of MA a week.
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    Fighting scale and PH creep

    Quote Originally Posted by RobbieH View Post
    A TA of 80 should help prevent pH drift better than a TA of 100 though.

    Do you only run the waterfalls when they are needed? If not, it might help to do so.

    I go through a gallon of MA a week.
    Very true.

    If rising pH is a problem, one additional lever a pool owner can use is to add borates to the pool. Borates increase the alkalinity only a small amount but buffer the water against rising pH (as opposed to carbonate alkalinity which buffers the water against falling pH). It doesn't reduce the overall amount of acid needed to maintain a specific pH but it lengthens the interval between acid additions.

    Adding borates can help keep the CSI in better balance by giving the pool owner a bit more margin with a pool's chemical addition schedule.

    However, borates should only be used once a pool owner has a good handle on their pool water chemistry and they can demonstrate consistently balanced water.



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    Re: Fighting scale and PH creep

    I run my filter 10 hours a day and the cleaner (polaris) 4 hours a day.
    The waterfalls run when the filter is on and in pool mode.
    I check my pool chemistry weekly (TA, FC, CC, CYA, anc CH) and PH daily.
    I test the salt level with test strips weekly.
    The pool temp is always in the 80s.
    I brush the pool weekly.

    When I hired a service my pool developed both green algae and scaling. That's when I threw the test strips away and bought the Taylor kit. I discovered I needed to add a ton of salt (over 11 bags) to make up for deficiency.

    If I can keep my PH around 7.4 with a little muriatic acid each week (my TA is now 110 and CH is now 210) I should be able to prevent scaling. I'm using the Taylor Water gram to keep my CSI in check. I'm so thankful for this website and everyone's help.

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    Re: Fighting scale and PH creep

    One thing I would say is that you really do not need to test salt levels weekly. As long as you have no major water volume changes, once per month is more than enough.

    If your salt level is changing weekly (decreasing) then you possibly have a water leak. Salt is a lot like calcium and CYA, those values do not change much over the course of a swim season.



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    Re: Fighting scale and PH creep

    I agree. The salt level has been stable since I added the 11 bags. No change in over two months. Monthly testing is appropriate.

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    Re: Fighting scale and PH creep

    I had scaling in the pool as well as the stone surface. I don't know what the PH was because I wasn't testing it when it started. My pool service was supposed to take care of adding chemicals, testing the water, brushing the pool etc. When I started to test the PH I soon discovered I had to add PH down frequently to keep it in check. I soon discovered Muriatic acid works as well if not better and is much cheaper.

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