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PH Struggles


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New to spa water care and to this site, I have a pretty specific situation that I'm struggling with and am kind of at my wits end.  I've read through a bunch of existing threads and tried a number of things to resolve, but have not yet found a solution to my problem.

I'll try to provide as much detail as possible and hopefully someone more knowledgeable than me about this stuff can help or even point me to an existing thread that could help!

In general, my issue is that balancing my PH the way I'm doing it now is nearly a full time job.

At initial fill, my water started out with the following attributes:

PH:  8.0+, initial acid demand test showed that .75oz of PH down should bring it to 7.5

TA: 100 ppm

Upon adding Sodium Bisulfate in .75oz increments to lower PH and waiting 6-12 hours in between, the PH did not change at all until roughly 6oz total was added over several days.  TA did decrease incrementally with each addition and eventually got to 50-60 ppm and the PH finally lowered to 7.6.  The tub then stayed relatively stable for a couple of weeks at which point the PH started to dive.  I was then forced to add Sodium Bicarbonate to bring it back up and essentially ended up adding back about as much Sodium Bicarbonate over the following week as I did Sodium Bisulfate to begin with until it stabilized again.  All during the process, I was careful to maintain Chlorine levels (using Dichlor) between 3-5ppm to avoid any false PH readings. 

To make things more complicated, after about a total of 10 weeks of constant maintenance, adjustment, and use, I shocked the spa (to 10+ppm chlorine) and the PH crashed and never recovered, even after chlorine levels dropped back to normal levels.  At this point, no matter how much Sodium Bicarbonate I added, I could not get the PH to increase.

Given that situation and given all the chemicals I had added along the way, I finally decided to just drain and start again hoping that my error was not waiting long enough for things to stabilize between adding chemicals.  Unfortunately, after re-filling, I am now a week into the same exact cycle as before, now waiting 24 hours between chemical additions with exactly the same results as the first fill so far.  

As more context, I have a 3 month old 340 gallon Hot Spring Relay spa with Ozonator.  When I originally filled the tub after installation, I had to decide whether to use water from my whole house softener or not.  Before filling, the calcium hardness of unsoftened water was very high and would have required a lot of expensive hardness decreaser to bring down, so I chose the cheaper route of using the softened water and then increasing the calcium hardness with inexpensive hardness increaser. 

Given some of the recommendations I've read in other threads, I've ordered some boric acid hoping that it may help stabilize the PH and will add as soon as it arrives, but given the huge swings in PH I'm seeing I'm not confident that will resolve my issues.

What am I doing wrong?

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First, please post what chemicals you are using (sanitizer, balancers, etc.) and post a full set of test results and how you obtained them (strips, a colorimeter (with strips, discs, or liquid or tablet reagents), a kit with liquid reagents (you mentioned using an acid demand test with indicates you are possibly using one of the Taylor or LaMotte test kits).

On 6/16/2022 at 12:29 PM, TubShark said:

Upon adding Sodium Bisulfate in .75oz increments to lower PH and waiting 6-12 hours in between, the PH did not change at all until roughly 6oz total was added over several days.  TA did decrease incrementally with each addition and eventually got to 50-60 ppm and the PH finally lowered to 7.6.

Why did it take so long? You need to aerate the water to gas off CO2 which, in turn, causes the pH to rise. Hot tubs are easy to aerate. Just uncover them, turn on all the jets, aerators, and bubbles if you have them and run the tub. The small volume of water in the tub will rise in pH quickly and you are starting with an initial TA of 100 ppm which is not very high to begin with. A few hours of aeration will cause a pH rise and then you drop it again and repeat.

Read these post for a better understanding of pH and TA:

https://www.poolspaforum.com/forum/index.php?/topic/52522-some-truths-about-ph-and-ta/

https://www.poolspaforum.com/forum/index.php?/topic/28846-lowering-total-alkalinity-howto/

 

Also constant use of dichlor will cause your CYA to rise too high quickly (dichlor adds 9 ppm of CYA for every 10 ppm of free chlorine added).

Crashing pH is usually associated with the use of trichlor which, IMHO, should never be used in a tub given the small volume of water and the extremely acidic nature of trichlor.

You never mentioned if your TA stayed relatively stable or also crashed. If you TA was in range then all you need to do to raise the pH is aerate the water (uncover the spa and run the jets and aerators to gas off CO2 and the pH will rise). You do not need to add more baking soda unless the TA is too low.

On 6/16/2022 at 12:29 PM, TubShark said:

To make things more complicated, after about a total of 10 weeks of constant maintenance, adjustment, and use, I shocked the spa (to 10+ppm chlorine) and the PH crashed and never recovered, even after chlorine levels dropped back to normal levels.  At this point, no matter how much Sodium Bicarbonate I added, I could not get the PH to increase.

What did you shock with, trichlor or dichlor? Shock levels of sanitizer will cause pH to read high when it's actually low, sometimes dangerously low. Once the santizer level drops you will see lower pH readings. Once again, you hae not posted any TA readings during this event. Baking soda (sodium bicarbonate) is not the best chemical to use to raise pH. A much better choice is borax (sodium tetreaborate decahydrate or pentahydrate). The decahydrate can be found in the laundry aisle of any grocery as borax and the pentahydrate is available at many pool and spa supply stores at a much higher price. If you go that route you want the product that requires acid be added with it and not the pH neutral product. Dose borax at approx twice the amoun that you would dose sodium carbonate (washing soda or pH increaser). Sodium carbonate will cause a sharp rise in TA which borax does not do. Unless you are using trichlor (in a swimming pool) then you have no need for sodium carbonate.

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