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Can’t get ph to rise with aeration


spf8298

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I have had alkalinity issues with my hot tub water.  I ordered the Taylor 2006 test kit and have been doing the acid demand tests trying to get my alkalinity lowered.  Before I started the process, my calcium hardness was 160, ph was 7.3, and alkalinity was 140.   I initially used 1.97 Oz of dry acid to bring the ph down to 7.0 and then I aerated for a half hour and retested ph.  It was still 7.0.  I then aerated for another half hour and retested ph and it was still 7.0.   I just can’t seem to get the ph to rise through aeration.  There’s plenty of turbulence in the water.   I’m no chemist, but I thought this would be easier.  Frustrated.   Does anyone have any suggestions for me?

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The following is a repost of the answer I gave to spf8298 in the PM he sent me. I asked him to repost in the forum so everyone can benefit from his question if they are having similar problems:

A TA of 140 will take a while to bring down at first, that is normal and as the TA drops it goes faster and takes less acid to drop the pH to 7.0,  which is why using the acid demand test is important, but there is a problem with your procedure that I will explain in a bit.

First, did you test the pH after dropping it and was it really at 7.0?  This is an important step. If you don't get the pH to 7.2 or 7.0 you are not adding enough acid to drop the TA. Why 7.0? Because dropping your pH below that can cause damage to your equipment. The total amount of acid needed to drop a TA of 140 ppm to about 60 ppm, if added all at once, would drop the pH dangerously low!

Now the part where you made your mistake . You need to aerate until the pH rises ABOVE 7.6 and then used the acid demand test to determine how much acid will drop it back down to 7.0, aerate until it's above 7.6, check TA, and repeat this until TA is at your target. Then adjust your pH to the desired level if needed by either adding enough acid to drop it to the level you want or aerating if it's too low.

At first the TA will not move by much and it will take a while aerating to get the pH back up but after a while the TA will start moving down and it will take less and less acid to drop the pH and less time aerating to bring it back up. The more efficient your aeration is the faster the process goes. Run the spa on high, open any air injectors, turn on bubblers and air blowers if you have them, turn your jets to break the surface of the water, and, it goes without saying, the spa needs to be uncovered.

This post should give you some helpful advice:

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

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11 hours ago, RDspaguy said:

How are you aerating? 

@waterbear, any clue?

I am aerating with the cover off and all jets on full.  Following waterbears comment,I failed to bring the ph up to 7.6 before starting.   I took the ph down from 7.3 to 7.0, testing before and after, and then began the aerating process.    Even with skipping aerating at first to bring ph to 7.6, I still don’t understand why I can’t get the ph to rise from 7.0. 

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You bring the pH up to 7.6 from 7.0 by aerating. If you started at 7.3 and dropped to 7.0 you aerate until the pH rises to above 7.6. Just keep aerating, it could tgake a day or so when you first start process, this is totally normal, and it takes patience which is something you cannot buy in a bottle and add to your water. Just keep aerating and check pH once a day until it rises. It eventually will. As you continue the process you will find that you need less and less acid to get to 7.0 and the pH will  rise much faster with aeration. You are doing fine.

To give you some perspective,If you tried to drop you TA to 60 ppm by adding the acid all at once you would need about 8.5 ounces of 31% muriatic acid but it would drop you pH to a VERY DANGEROUS 3.0!!!!!!!! DO NOT TRY THIS!!!!!!! 11.5 oz of ldry acid added all at once would lower the TA about the same but drop the pH even lower!!!!!!!!

The SAFE way is to drop the pH to 70, Aerate until the pH rises above 7.6 (no time limit, just keep aerating until the pH rises), test TA (it will not move at all in the beginning), and repeat until the TA drops! it might take several days to a week or so, depending on how high the initial TA is and an initial TA of 140 ppm is high.

FWIW, even without aeration the pH will rise but it takes longer. Aeration just speeds up the process.

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point the jets so they break the surface of the water. If you have air injectors or bubbles turn then on full. You don't want to just move the water around, you want to create as much surface action and turbulence as possible. You can even get into the spa and splash someone for 10 or 20 minutes and let them spash you back, Just keep the water IN the spa!

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45 minutes ago, waterbear said:

You bring the pH up to 7.6 from 7.0 by aerating. If you started at 7.3 and dropped to 7.0 you aerate until the pH rises to above 7.6. Just keep aerating, it could tgake a day or so when you first start process, this is totally normal, and it takes patience which is something you cannot buy in a bottle and add to your water. Just keep aerating and check pH once a day until it rises. It eventually will. As you continue the process you will find that you need less and less acid to get to 7.0 and the pH will  rise much faster with aeration. You are doing fine.

To give you some perspective,If you tried to drop you TA to 60 ppm by adding the acid all at once you would need about 8.5 ounces of 31% muriatic acid but it would drop you pH to a VERY DANGEROUS 3.0!!!!!!!! DO NOT TRY THIS!!!!!!! 11.5 oz of ldry acid added all at once would lower the TA about the same but drop the pH even lower!!!!!!!!

The SAFE way is to drop the pH to 70, Aerate until the pH rises above 7.6 (no time limit, just keep aerating until the pH rises), test TA (it will not move at all in the beginning), and repeat until the TA drops! it might take several days to a week or so, depending on how high the initial TA is and an initial TA of 140 ppm is high.

FWIW, even without aeration the pH will rise but it takes longer. Aeration just speeds up the process.

I understand that you don’t want ph to be on acidic side.  I’m not an idiot.  I just didn’t think you’d have to aerate all day to get ph to rise to 7.6.   Especially when the tub cycles off ever 15 minutes.   This tub has been worse than raising a newborn, and I have three of those.   
 

It’s 17 degrees here today, I would assume you have to aerate with cover open?  Gonna watch the electric meter spin today.  

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23 hours ago, spf8298 said:

 I just didn’t think you’d have to aerate all day to get ph to rise to 7.6.  

What you think and  reality are not always the same. Initially it could take more than a day if the aeration is not efficient. If your tub has blowers and air injectors  or a handheld shower head that attaches to a jet (a tub that I owned once had one) and the jets can be adjusted to break the surface of the water for maximum turbulence then aeration will go quickly. If your tub does not have these things and the water just moves around but there is not a lot of surface turbulence then it can take significantly longer.

23 hours ago, spf8298 said:

I would assume you have to aerate with cover open

Let me ask you this. Will a bottle of soda lose it's carbonation if you keep it capped? You are trying to make the water lose it's carbonation. The tub needs to be uncovered to allow CO2 to outgas.

As an alternative, don't worry about the TA during the cold weather and when the pH rises above 7.6 drop it to 7.0 and just enjoy the tub. The TA will eventually drop but you will find that the pH rises quickly in between tub usage. As the TA begins to drop you will see the pH stays stable for a longer time before it rises.

 

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  • 2 years later...

Usually just turning on the air intake all the way and running the tub uncovered on high speed (and turning on bubblers if you have them) will aerate. You want to turn the jets upward so you break the water surface. You could put a small submergable pump in the tub with a pvc pipe attached so the water shoots up and then falls back into the tub like a fountain but I've never really seen a tub that needed that much additional aeration. It's usually pools that might need additional help.

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5 hours ago, waterbear said:

Usually just turning on the air intake all the way and running the tub uncovered on high speed (and turning on bubblers if you have them) will aerate. You want to turn the jets upward so you break the water surface. You could put a small submergable pump in the tub with a pvc pipe attached so the water shoots up and then falls back into the tub like a fountain but I've never really seen a tub that needed that much additional aeration. It's usually pools that might need additional help.

OK, it's just annoying because my hot tub is an acrylic above ground one so there is not much I can add to it and the control panel on it only allows for the air and bubbles to run for 15 minutes. And because I live in Canada and it can be -40 in the winter I don't want to go out there every 15 minutes haha.   But for now I'll just keep going out and pressing the button.  I was hoping there was an easy thing that would just let me drop it in, let it run for a few hours and then pull out and pack up until next time I need it. 

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18 hours ago, Testinglife said:

I was hoping there was an easy thing that would just let me drop it in, let it run for a few hours and then pull out and pack up until next time I need it. 

You could put a small submergable pump in the tub with a pvc pipe attached so the water shoots up and then falls back into the tub like a fountain

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