Quick hot tub TA question

KS Mike

Bronze Supporter
May 2, 2017
25
Wichita, KS
I’ve had a pool for a few years but recently bought a hot tub. As far as TA goes, if it’s low and I add baking soda, it will raise the ph. If I then add acid to bring it down, that coupled with the aeration of the jets seems like it would just lower the TA and I’ll be stuck in an endless cycle of additions.

is there something I am missing? I have lowered the TA in my pool using the aeration method many times and this seems like it would have the same effect.
 

Jimrahbe

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Jul 7, 2014
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Mike,

I never do anything to "adjust" my TA, unless it drops below 50 ppm.. I just use a little acid to keep my pH somewhere in the 7's and I am done...

Thanks,

Jim R.
 
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KS Mike

Bronze Supporter
May 2, 2017
25
Wichita, KS
What is the TA of your fill water? How does your pH trend over time and use?
Fill water had a TA of 80, ph of 8.2. I’ve been adding acid over a 24 hr period and finally got down to 7.4 but the TA is now 20 which seems really low (at least based on my pool experience). Maybe I just need to wait a day or two, and let things settle out and see where I end up.

I just got the hot tub in December (it was a floor model) and did a quick purge with ahh some then got it balanced without much problem. Over the month I was having an unbelievable time keeping chlorine in it for more than a few hours, which I think was partly due to it being sold with a used up salt cell. I ended up with a few small areas of rash and just decided to start over with everything fresh. I did 4 purges with ahh some, 2 with spa serum cleaner, and 1 with both. I even let one purge sit overnight. Shocked to 25 with each, and hyper chlorinated for 1 hour on the last (maybe overkill but I’m a little obsessive about water quality). I got a lot of green sludge out that gradually decreased with each purge to nothing. So hopefully it’s cleaned out, but I plan on running the chlorine on the high side for a while and have a new cell for it.

Anyways...the first fill I did not have problems with the TA or ph once it was balanced, so not sure what happened this time. I’ll check it again in the morning and see where it’s at. So far I am finding pools easier than hot tubs.
 

KS Mike

Bronze Supporter
May 2, 2017
25
Wichita, KS
What is the TA of your fill water? How does your pH trend over time and use?

That’s what I have always done with the pool, but my TA is 20 (actually started to change color on the first drop so maybe between 10 and 20). I just don’t have experience with jets aerating the water so much. Maybe I just checked it after adding too much too fast. I’ll check it in the morning and see what the numbers look like.
 

jseyfert3

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That’s what I have always done with the pool, but my TA is 20 (actually started to change color on the first drop so maybe between 10 and 20). I just don’t have experience with jets aerating the water so much. Maybe I just checked it after adding too much too fast. I’ll check it in the morning and see what the numbers look like.
Proper procedure is to go till the color doesn’t change any further, then don’t count the drop that doesn’t count further color change.

So your TA is probably at least 30.

How high are you letting the pH rise before adding acid and how low are you targeting when you add acid?

Maybe I just checked it after adding too much too fast. I’ll check it in the morning and see what the numbers look like.
Perhaps, but if I run both my hot tub pumps on high with the diverters set to run water to all jets (how I leave it when it’s not actively being used) everything is fully mixed within like two minutes, if not sooner.

If you were testing but did not run your pumps to mix it quickly then it could be a false reading.
 

KS Mike

Bronze Supporter
May 2, 2017
25
Wichita, KS
Proper procedure is to go till the color doesn’t change any further, then don’t count the drop that doesn’t count further color change.

So your TA is probably at least 30.

How high are you letting the pH rise before adding acid and how low are you targeting when you add acid?


Perhaps, but if I run both my hot tub pumps on high with the diverters set to run water to all jets (how I leave it when it’s not actively being used) everything is fully mixed within like two minutes, if not sooner.

If you were testing but did not run your pumps to mix it quickly then it could be a false reading.
Thanks for the info, I did not know that about the color change and extra drop. I’m shouting for 7.6.

So for an update I woke up this morning to a TA of 10, and ph of 6.8. I thought maybe I had messed up a test so repeated and got the same result. I thought it was great because now the numbers made sense at least. I thought I could raise the TA and ph and be perfect. Plugged the numbers into pool math and added the prescribed amount of baking soda (I even weighed it), ran the jets for 1 hour and no change, repeated and had little change, repeated and again little change in ph but TA was falling again.

I had accidentally ordered ph increaser from Amazon last week so I decided to switch to it. Added what it said on the back of the bottle which got me up to 7.0 or so. Added more and the next check ph was at least (likely over) 8.2 with a TA of 40. So now I’m back to the acid....again and again and again. Once I get it close to 7.6 I’m going to check the TA for curiosity, but I’m not going to try and achieve a set number on TA. Never have I had this much problem with water. It doesn’t move then just swings in the opposite direction.

I may look into just using muriatic acid instead of the dry stuff. I have spent the whole day just trying to get the ph right, waiting at least an hour between checks.at least with it I know it’s dissolved.

I would like to add boric acid to it, but not until things settle down and level out.
 

jseyfert3

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This behavior seems odd, especially the TA and pH falling overnight.

So to clarify you’ve been adding dry acid?How are you adding chlorine? Are you adding anything else?

I thought I could raise the TA and ph and be perfect. Plugged the numbers into pool math and added the prescribed amount of baking soda (I even weighed it), ran the jets for 1 hour and no change, repeated and had little change, repeated and again little change in ph but TA was falling again.
Again that TA drop is odd...

Baking soda doesn’t affect pH much, it much more strongly affects TA. My understanding is it should be used to increase TA, then after TA is up to desired use aeration to raise pH. On a hot tub this is running jets with air valves open.

I don’t know for sure but I’m assuming pH increaser is washing soda (sodium carbonate). This will also raise TA, but unlike baking soda (sodium bicarbonate) it will have an immediate and pronounced affect on pH.

Fun fact you can make washing soda by baking baking soda at a few hundred degrees in the oven for an hour or so (google if curious, I’ve done this but it’s been a while). You can also buy washing soda from the laundry aisle at some stores.

I may look into just using muriatic acid instead of the dry stuff. I have spent the whole day just trying to get the ph right, waiting at least an hour between checks.at least with it I know it’s dissolved.
In general muriatic acid is the preferred route, as it does not contain sulfates that dry acid (sodium bisulfate) does. Sulfates will cause some amount of additional corrosion to metals, i.e. the heater in a hot tub (usually the only metal exposed to water). It is harder to measure small amounts though.
 

KS Mike

Bronze Supporter
May 2, 2017
25
Wichita, KS
This behavior seems odd, especially the TA and pH falling overnight.

So to clarify you’ve been adding dry acid?How are you adding chlorine? Are you adding anything else?


Again that TA drop is odd...

Baking soda doesn’t affect pH much, it much more strongly affects TA. My understanding is it should be used to increase TA, then after TA is up to desired use aeration to raise pH. On a hot tub this is running jets with air valves open.

I don’t know for sure but I’m assuming pH increaser is washing soda (sodium carbonate). This will also raise TA, but unlike baking soda (sodium bicarbonate) it will have an immediate and pronounced affect on pH.

Fun fact you can make washing soda by baking baking soda at a few hundred degrees in the oven for an hour or so (google if curious, I’ve done this but it’s been a while). You can also buy washing soda from the laundry aisle at some stores.


In general muriatic acid is the preferred route, as it does not contain sulfates that dry acid (sodium bisulfate) does. Sulfates will cause some amount of additional corrosion to metals, i.e. the heater in a hot tub (usually the only metal exposed to water). It is harder to measure small amounts though.

yes I have been adding dry acid as the amounts of muriatic acid seem so small. I’ve also added about 1/2 of my dichlor (for a CYA of 30) before switching to bleach. Other than that I’ve added salt to the lower end of the range, used the Hotsprings calcium remover pillow to get to their recommended 50 ppm. Other than that, nothing. No one has been in the hot tub for over a week. Jets have been running a lot with all the repeat doses.

It is odd to say the least, but what you just said may partially explain it. I started adding baking soda and saw the TA rising but not much ph change. Then I switched to the sodium carbonate which is when I saw the huge spike in ph.

I was beginning to rationalize it as the ph would not increase until the TA had risen to a point to “allow” it. Your idea explains it a little more. I was not aware of the differences between the two as I have never had to increase ph in my pool. It always drifts higher on its own with the salt chlorine generator, so my only experience is adding muriatic acid.

Its possible I was too heavy handed with the dry acid last night as well (after a week and a half of cleaning I’m just ready to have this thing working). It seems to be taking way more acid than it is supposed (that happened on the first fill also) to take which I assumed was due to the aeration bringing the TA down and ph up, then I added more acid and the same thing happened, until the TA was really low then the ph moves down in a wild swing.

i did check again tonight and things seem stable. I’ll check again in the morning and fine tune (hopefully that is all I need to do) then I can move on to figuring out if the cleaning and replacing the SWCG cell has fixed the chlorine issue.

What is the normal chlorine loss in a hot tub that is not being used? Seems like I read 25% in 24 hours but now I can’t seem to find that.
 

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KS Mike

Bronze Supporter
May 2, 2017
25
Wichita, KS
Finally making progress. There was no change over night. Ph is still 7.8 with a TA of 30, and chlorine increased from 9 to 10.5 with the cell at its max setting so either the obsessive cleaning, the new cell, or both appears to have fixed that problem. Prior to last night I have never seen an increase in chlorine overnight and was happy if there was any chlorine by morning, if there was it was usually 1 or less.

So what would you do about the ph and TA now?
 

KS Mike

Bronze Supporter
May 2, 2017
25
Wichita, KS
And I apologize I went back and read my previous post and noticed I said TA was falling with baking soda which I am sure led to confusion. TA was increasing with baking soda, but ph was not moving much. Not sure what I was thinking when I typed that.
 

Mdragger88

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Jun 1, 2018
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I dunno if jsey is up yet but i just read your whole thread. I would add a little baking soda to raise ta to 50 - use PoolMath for calculating additions. Also be sure you’re not over shooting your volume - that could lead to the larger changes than u are expecting. Then leave ph alone. When it gets to 8 lower it to 7.6 w/ ma but maybe go a little shy on the dose to tweek your actual volume calculations.
 

Mdragger88

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Also be weary of the acidic effects of dichlor & take them into consideration- poolmath effects of adding will show u
 

jseyfert3

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used the Hotsprings calcium remover pillow to get to their recommended 50 ppm
I'm not sure what's in this. Do you have a high fill CH such that you have a positive CSI?

What is the normal chlorine loss in a hot tub that is not being used? Seems like I read 25% in 24 hours but now I can’t seem to find that.
This is tough to answer. Not being used really takes a while to get there. After a night of heavy use (3-4 people for hours at 100 °F) I can see increased chlorine demand for well over a week as residual bather waste is slowly broken down. Usually we use the tub again before it returns to a "baseline" number.

I think the best I recall is from our previous tub, an inflatable Intex. Due to the fact that it couldn't maintain temp on the days when it's best to use (cool fall or calm winter nights) it never got near the usage our 6 person Cal Spas does. No long nights with multiple people drinking for hours. On that I think the lowest drop I remember is somewhere around 20% in 24 hrs (10 ppm to 8 ppm), but it's been a couple years so my memory is foggy.

On my Cal Spas with a Saltron Mini SWCG I don't usually measure drop, the SWCG maintains chlorine when not being used so I just check and add the first few days after a heavy use, then check every few days to a week when not used to see how the SWCG is keeping up.

Finally making progress. There was no change over night. Ph is still 7.8 with a TA of 30, and chlorine increased from 9 to 10.5 with the cell at its max setting so either the obsessive cleaning, the new cell, or both appears to have fixed that problem. Prior to last night I have never seen an increase in chlorine overnight and was happy if there was any chlorine by morning, if there was it was usually 1 or less.

So what would you do about the ph and TA now?
Honestly I may just leave it for the moment and see what happens. You mentioned borates and they may be useful. I haven't used them in our Cal Spas yet, I tried them in our Intex one but that didn't have much aeration, I was going for the "feel" some talk about with borates. Didn't notice that, so they'd be purely to slow pH swings in the Cal Spa.

Also be weary of the acidic effects of dichlor & take them into consideration- poolmath effects of adding will show u
Yes, this is an excellent point, and why I asked what you were adding. Dichlor is acidic and will lower pH. Honestly I've personally stopped using dichlor then bleach method. I have straight solid CYA for my pool, and I can add this and it doesn't affect pH much at all. Unlike a pool CYA dissolved in a hot tub pretty fast (hours), so I don't use a sock and just dump it in near the filter so the water action helps dissolve it.
 

KS Mike

Bronze Supporter
May 2, 2017
25
Wichita, KS
I'm not sure what's in this. Do you have a high fill CH such that you have a positive CSI?


This is tough to answer. Not being used really takes a while to get there. After a night of heavy use (3-4 people for hours at 100 °F) I can see increased chlorine demand for well over a week as residual bather waste is slowly broken down. Usually we use the tub again before it returns to a "baseline" number.

I think the best I recall is from our previous tub, an inflatable Intex. Due to the fact that it couldn't maintain temp on the days when it's best to use (cool fall or calm winter nights) it never got near the usage our 6 person Cal Spas does. No long nights with multiple people drinking for hours. On that I think the lowest drop I remember is somewhere around 20% in 24 hrs (10 ppm to 8 ppm), but it's been a couple years so my memory is foggy.

On my Cal Spas with a Saltron Mini SWCG I don't usually measure drop, the SWCG maintains chlorine when not being used so I just check and add the first few days after a heavy use, then check every few days to a week when not used to see how the SWCG is keeping up.


Honestly I may just leave it for the moment and see what happens. You mentioned borates and they may be useful. I haven't used them in our Cal Spas yet, I tried them in our Intex one but that didn't have much aeration, I was going for the "feel" some talk about with borates. Didn't notice that, so they'd be purely to slow pH swings in the Cal Spa.


Yes, this is an excellent point, and why I asked what you were adding. Dichlor is acidic and will lower pH. Honestly I've personally stopped using dichlor then bleach method. I have straight solid CYA for my pool, and I can add this and it doesn't affect pH much at all. Unlike a pool CYA dissolved in a hot tub pretty fast (hours), so I don't use a sock and just dump it in near the filter so the water action helps dissolve it.
 

KS Mike

Bronze Supporter
May 2, 2017
25
Wichita, KS
Thanks guys. I don’t know what is in the pillow either and I tried to find out because they are ridiculously expensive. I think I’m just going to buy a portable water softener for future fills. To be honest there is a lot about the spa I’m a little hazy on like why CH has to be so low for the SWCG to work? Why is the cell only good for 4 months?

I think I’ll just hold off on any more additions for a few days at least and see where the water goes. I imagine the ph will drift higher, maybe the dichlor I still have to add will help that. If I need it I’ll stick to baking soda to try and get the TA up some. I might go with pure CYA on future fills since it’s laying around also. One less thing to mess with the ph.

It also occurred to me that I can be less than precise on a big pool and be ok, but that likely won’t work on a hot tub.

Thanks again
 
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