Struggle to lower pH after salt water conversion

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SirNoSplashing

Member
Jul 17, 2022
24
Ohio
Hello, I have a 450G hot tub, ~4 years old. Once I got my new IG pool with SWG, I loved it so much I decided to convert my hot tub with the Saltron Mini. It was worth the $300 to me to give it a shot.
After I replaced the water recently, I got the salinity to 2400 per the recommendation from Solaxx. I manually added chlorine to jump it to the 3-5ppm level, and with the Saltron its been maintaining (I adjusted the settings over the course of a few days until I got about the same reading each day). I adjusted the Alkalinity and pH at the onset as well, and when I tested pH recently, I still read around 7.8 per my Taylor K-2006C kit. This is not uncommon for me with fresh water fills. Only this time when I added 2 Tbsp of pH decreaser (Sodium bisulfate) it had no impact. Then I tried again, with again seemingly no impact. Now a number of days has past. Tomorrow I have new pH decreaser on the way, though the bottle I have is only ~3 years old if I could guess. Taylor kit is new and within the dates. I have used it effectively in the past for pH.

Is this something to do with the Salinity content? Any risk to continuing to add pH decreaser? My alkalinity measures about 100ppm. What are other factors which could make it difficult to lower pH?

Thanks in advance for any advice you can give.
 
Sodium bicarbonate decomposes into sodium carbonate, carbon dioxide, and water:
2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g)

Sodium bicarbonate powder is stable below 76%RH at 77°F and below 48%RH at 104°F, respectively. Exceed these it will degrade.*

Where do you store your pH decreaser? Where in Ohio do you live?

*Kuu, W.-Y., Chilamkurti, R., & Chen, C. (1998). Effect of relative humidity and temperature on moisture sorption and stability of sodium bicarbonate powder. International Journal of Pharmaceutics, 166(2), 167–175. Redirecting
 
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When are you remeasuring the pH after you add the decreaser?

Your TA is quite high for a hot tub. In my experience, unless you are closer to TA of 40-60ppm your pH will jump back up in a matter of a few hours. If you are dropping pH down to 7.6, and then remeasuring in like 4 hours to check, I wouldn't be surprised if your pH is closer tp 7.8.or even higher. In 12 hours it would probably be 8.0+.
 
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Krulligo said:
When are you remeasuring the pH after you add the decreaser?

Your TA is quite high for a hot tub. In my experience, unless you are closer to TA of 40-60ppm your pH will jump back up in a matter of a few hours. If you are dropping pH down to 7.6, and then remeasuring in like 4 hours to check, I wouldn't be surprised if your pH is closer tp 7.8.or even higher. In 12 hours it would probably be 8.0+.
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Thank you for this. the place I bought my spa from always recommended a higher range on their test reports (I test on my own now), and I have always been using that as a target. So, with new water I always add alkalinity increaser / baking soda... and I probably should not be doing that. I want to say it was naturally around 40-50 before I added anything. I guess I am fighting that?

How do you lower it? Just keep hitting it hard with pH decreaser? My new bag just arrived today.

EDIT: why do all of the generic guides online say 80-120ppm for alkalinity for a hot tub?
 
I think that range is taken from what you want in a pool but hot tub is different mainly because it's such a small body of water and gets lots of aeration.

Honestly you just need to find the "sweet spot" of what your tub needs to become stable. This depends on if you do chlorine vs bromine, how often the tub is used by how many people, how your filtration and jet cycles are set up, etc. But from my experience and of others on here, a much lower TA is preferred for hot tubs.

You lower your TA as you are lowering your pH. So right now if you find that your pH is drifting very fast (if you drop it to 7.6 and then next day you are measuring 8+) then don't bother with readjusting it back to 7.6, but hammer it down to 7.0. this will lower your TA much faster, and you keep doing this until one day you wake up and you are like, hey my pH didnt go up to 8+ this time but it's at 7.8. Then at this point do smaller adjustments, so drop it down to 7.4, maybe the next day it will be 7.6. If then this becomes stable and your pH stays between 7.6-7.8, you are set to go. Measure up your TA at this point and that is the TA your tube maintains a stable pH of 7.6-7.8 at. If the TA is higher than 40ppm you are golden. If it's below you might want to consider something like borates to stabilize pH at a slightly higher TA, or you just need to do more frequent but minor pH adjustments.
 
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Krulligo said:
I think that range is taken from what you want in a pool but hot tub is different mainly because it's such a small body of water and gets lots of aeration.

Honestly you just need to find the "sweet spot" of what your tub needs to become stable. This depends on if you do chlorine vs bromine, how often the tub is used by how many people, how your filtration and jet cycles are set up, etc. But from my experience and of others on here, a much lower TA is preferred for hot tubs.

You lower your TA as you are lowering your pH. So right now if you find that your pH is drifting very fast (if you drop it to 7.6 and then next day you are measuring 8+) then don't bother with readjusting it back to 7.6, but hammer it down to 7.0. this will lower your TA much faster, and you keep doing this until one day you wake up and you are like, hey my pH didnt go up to 8+ this time but it's at 7.8. Then at this point do smaller adjustments, so drop it down to 7.4, maybe the next day it will be 7.6. If then this becomes stable and your pH stays between 7.6-7.8, you are set to go. Measure up your TA at this point and that is the TA your tube maintains a stable pH of 7.6-7.8 at. If the TA is higher than 40ppm you are golden. If it's below you might want to consider something like borates to stabilize pH at a slightly higher TA, or you just need to do more frequent but minor pH adjustments.
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Ok I have slowly dropped TA to 70ppm (just rechecked it after trying to lower pH the past few days), pH still bright pink on mt Taylor kit. So tonight I will "shock" it down, I will use the calculator to jump from 8 to 7.0 pH.

Edit: the calc is saying 1.9oz by weight or 1.2oz by volume of dry acid given my current levels. I will give that a shot.
 
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Krulligo said:
Also make sure your chlorine is below 10ppm when measuring pH. I'm sure it is but if your chlorine level is really high you will also get a bright pink/purple pH reading even if your pH is within range
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Again, I can't thank you enough for the insight. So, after adding 1.9oz (weight) of pH reducer yesterday, my TA is now 60, and pH is less pink... but certainly not orange like you start to see at 7.6. If I could guess I am around 7.8 or slightly lower. Given your last advice, I have a better shot of inching down to the 7.4-7.6 range now. Math says 0.5oz by weight to go from 7.8 to 7.4.
 
Glad it's working out for you and stabilizing now. pH 7.8 or lower is within the range you want. Typically for hot tubs, you want it to be 7.6-7.8. I think at 60 TA you are going to see a lot more stability, so now only do minor adjustments to pH when needed. I wouldn't be worried at 7.7-7.8 at all. But see in 2 or 3 days whether it stays at this range. If it rises slightly adjust it back down to pH 7.6 (and maybe a TA of 50 will be alot more stable for you). But if you are stable at 7.7-7.8 you are good to go, and only really need to measure pH maybe once a week, and do very minor adjustments once in a while.
 
SirNoSplashing said:
EDIT: why do all of the generic guides online say 80-120ppm for alkalinity for a hot tub?
Click to expand...
Likely because the guides are from pool ls where they advocate for using trichlor tablets to chlorinate the water. The acid in the trichlor forces the TA and pH down over time and you could crash the pH to dangerous levels if it gets too low. It’s one of the reasons why TFP doesn’t recommend long term use of trichlor.
 

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Krulligo said:
Glad it's working out for you and stabilizing now. pH 7.8 or lower is within the range you want. Typically for hot tubs, you want it to be 7.6-7.8. I think at 60 TA you are going to see a lot more stability, so now only do minor adjustments to pH when needed. I wouldn't be worried at 7.7-7.8 at all. But see in 2 or 3 days whether it stays at this range. If it rises slightly adjust it back down to pH 7.6 (and maybe a TA of 50 will be alot more stable for you). But if you are stable at 7.7-7.8 you are good to go, and only really need to measure pH maybe once a week, and do very minor adjustments once in a while.
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thanks.

as an update, my TA is now 50, but pH still looks 7.8-8.0 to me. "hot pink" is how I would describe the color via the Taylor kit. I will wait it out a bit and keep an eye on it. At this point I have put quite a bit of dry acid into the tub, and the TA has gone down for sure.
 
SirNoSplashing said:
thanks.

as an update, my TA is now 50, but pH still looks 7.8-8.0 to me. "hot pink" is how I would describe the color via the Taylor kit. I will wait it out a bit and keep an eye on it. At this point I have put quite a bit of dry acid into the tub, and the TA has gone down for sure.
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Can you take a pic of the color and comparitor. Also how high is your chlorine or bromine?
 
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Krulligo said:
Can you take a pic of the color and comparitor. Also how high is your chlorine or bromine?
Click to expand...

Hopefully the attachments work. One picture I am holding up to the window / overcast sky so its backlit naturally (5785). One is with a white cabinet as the background (5786)
Sky background for sure looks 8.0. Indoors I could argue its maybe closer to 7.8. Notably nothing like 7.6 IMO

Up to this point, I have added about 10 Tbsp by volume in 2 Tbsp increments (11/7-11/13), back then I was trying to inch my way down on pH.
Then I got new pH decreaser, and based on this thread, attempted to jump down heavily. I started going by weight, and added 1.9oz (11/15), then again 0.6oz the next day (11/16).

So, that is how much pH decreaser I have added thus far. Seems like a lot but maybe not? Not sure what to do next.

FYI - TA is remaining stable at 50.
 

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Krulligo said:
How are you calculating how much ph decreaser to add? Are you going by the Acid Demand test from the testing kit?
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PoolMath

Discover the calculator behind the perfect pool, PoolMath. Dealing with pools has allowed TFP to become the original authors of the best calculator on the net.
www.troublefreepool.com

Also used previous test results and recommendations from my local hot tub supplier / pool shop. They do testing and print out a report of what to add. Generally the TroubleFree Calc linked above seemed aligned with corrections I had made in the past via the local shop. Though this time with seemingly little impact.

I will say, I never had the Taylor kit for the hot tub (until I got my pool). So, I trusted the hot tub shop, made the corrections, and just moved on. I am not sure how effctive I have ever been at controlling pH.
 
Calculator is not the best since you are always guestimating measured pH. It's not bad if its in range, but anything that looks like pH 8 or above you really have no idea what it's at. Also, your pools water may have other components that is not taken into account by the calculator. Doing the acid demand test with the kit tells you exactly how much acid you need to drop your pH down to a certain level in your specific water. It should be a lot more accurate.

Still, this does not account for your rapid pH rise. So you are at TA =50 ppm, you can try going a bit lower but don't go below 40.

A few questions:

1) Do you keep your air controls closed on all your jets when the spa is not in use?
2) How often would you say your spa is used?
3) Have you considered adding borates to help with pH drift?
 
Krulligo said:
Calculator is not the best since you are always guestimating measured pH. It's not bad if its in range, but anything that looks like pH 8 or above you really have no idea what it's at. Also, your pools water may have other components that is not taken into account by the calculator. Doing the acid demand test with the kit tells you exactly how much acid you need to drop your pH down to a certain level in your specific water. It should be a lot more accurate.

Still, this does not account for your rapid pH rise. So you are at TA =50 ppm, you can try going a bit lower but don't go below 40.

A few questions:

1) Do you keep your air controls closed on all your jets when the spa is not in use?
2) How often would you say your spa is used?
3) Have you considered adding borates to help with pH drift?
Click to expand...

1) pretty sure I don't have air controls ? Its a Bullfrog spa. Had to google that.
2) honestly, and this is sad, I can't remember the last time I was in it. Now that cold weather is here, we intend to use it more... which motivated me to convert to SWG
3) no - I will google and begin to educate myself.
 
The air controls are all the knobs that are above the water line. If you turn them, they make the jets feel more powerful. Most people think these are to turn the jets on or off but in reality the amount of water the runs through the jets is always the same, you are just controlling how much air is mixed with the water which makes them feel more powerful. If you are leaving these air control knobs open when the spa is not used, the spa turns on many cycles throughout the day to circulate the water in your tub. Mixing air with water naturally increases your pH. So what you want to do is minimize this by keeping your air controls closed off when spa is not in use (so that only water is cycling out of the jets and doesn't mix with air)
 
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