New Spa Question or Observation - TA and PH

brajgreg

Well-known member
Apr 28, 2012
80
Houston, TX
I recently moved to Houston, and I bought a hot tub a couple of weeks ago for these cold winters and mild summers :p Anyway, I've had two other houses with two different pools, and have used the TFP method without a hitch. So far, everything is going fine with my spa (water is clear as can be), but I've still got some questions I suppose. Here are the details.

Dr. Wellness G-14 Spa - 450 gal, 92 total jets, 3 6HP pumps, waterfall, 92"x92"x36"
Water Chemistry 1/8/17:
FC - 5.5
PH - 8 (2 drops of acid demand got me to 7.6)
TA - 60
CH - 200
CYA - 30-35
Borates - 50 (Haven't actually measured--simply added 15 oz of boric acid recently)
Temp - 85 (Knew I wouldn't be in it over the weekend so I turned it down)

Problem #1: So I've been fighting this PH getting up to 8. The way I read the chlorine spa sticky was that if you have your TA down far enough, the jets won't tend to cause the PH to drift up that quickly. Whether my TA is 50 or 60, if I get in the spa and turn the jets on for about 30 minutes, my PH will be 8. If my TA is 50 or 60, should my PH be going up after a short time with the jets on? Granted, when I get in, 2 if not 3 of the pumps are on, and I like to open the aerator valves to get a better massage. Anyway, that's problem number one--PH rising more than expected for my TA level--but maybe that's normal and the sticky is ambiguous on this point (in my opinion)?

Problem #2: My supposed volume is 450 gallons. However, if I go to the pool calculator and I want to raise my chlorine 3 ppm, it says I need 60mL of 8.25% bleach. However, if I add 60mL and re-measure an hour or so later, I get an increase of about 5 ppm. I've tried it twice just to see. So for pool calculator purposes, I've been saying I have a 400 gal hot tub, but maybe I should say it's even less? because of problem #3.

Problem #3: So, I'm now using 400 gallons as my volume. Given a TA of 60 and a borate of 50, I'm to add 39 ml of 31.45% Muriatic Acid. I bought some graduated cylinders for $5 on amazon, and I measured out 39 ml, and dumped it in. But I also see that it's going to put my TA below 50, so I add about 10g of baking soda to bring my TA to 50. I checked today, and my PH was 7.4 (lower than expected) and my TA was 50 (expected). Now, with the TA test, it could be anywhere from like 45 to 55ish, right? But the PH dropping to 7.4 again makes me think that maybe I should be using less volume for the pool calculator than what the manufacturer says? I don't have exact numbers, but I know every time I add acid, it drops farther than expected. The outside dimensions match what they say they should be, but I question the volume. Maybe I'll get a fill meter or something.

Finally, when plugging my current values into the pool calculator vs goal values, I see that my CSI with the numbers provided above is exactly 0. Which seems pretty good, but the PH is 8 which is out of range. Then I see if I lower my PH to 7.6 and TA to 50, it reduces my CSI to -.39 which is still in the ok range, but a 0 looks pretty good, right? I think the answer here is that I need to get my PH in range and not be super concerned with the CSI. It’s a fiberglass spa anyway. This was just an observation.
Thanks for reading and for any help. All comments, hints, tips, tricks, or additional questions are appreciated. And finally, Roll Tide!

PS: for some reason, it won't let me update my signature to remove the old info and update with new :S
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
18,835
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
By chance are you measuring pH after adding bleach?

We normally say that bleach is pH neutral but that's technically not true. It is slightly caustic and adds to the TA over time. If you measure pH right after adding bleach in a clean hot tub, then you could be detecting the pH rise from adding the bleach.

Since you have borates in the water and some CYA, you could drop your TA down to 40ppm which would put you at a very low bicarbonate level. See if that helps at all.



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brajgreg

Well-known member
Apr 28, 2012
80
Houston, TX
By chance are you measuring pH after adding bleach?

We normally say that bleach is pH neutral but that's technically not true. It is slightly caustic and adds to the TA over time. If you measure pH right after adding bleach in a clean hot tub, then you could be detecting the pH rise from adding the bleach.

Since you have borates in the water and some CYA, you could drop your TA down to 40ppm which would put you at a very low bicarbonate level. See if that helps at all.



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I always measure first before adding anything (unless I just hopped out of the tub--then I just add a few ounces and measure again the next day).

I've been wondering since I have Borates in there as a buffer if I should consider lowering my TA any farther, but I've seen people saying multiple times to keep it 50 or higher. If/when I drift back up to 8, I'll add the acid and let it get to 40 and see how it goes.

Thanks!
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
18,835
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Cyanurates, borates and carbonates all act as pH buffers. Just keep a close eye on your pH if your TA goes down to 40ppm. You don't want to crash your pH.

Your tub is fiberglass so CSI is not too important. Just try to keep your CSI between -0.6 and 0. Your CSI will only be very negative when acid is first added, then it should recover and. E fine. As long as you keep your CH levels at or near the recommended values for FG, your shell should be fine.

As for volume, spas are always spec'd with their maximum fill volume. People rarely ever fill them that much. There are chemical methods to get an exact volume of the spa but that requires the use of lots of TA reagent. You could just by a cheap, hose end flow meter and measure the volume next time you fill it up.


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brajgreg

Well-known member
Apr 28, 2012
80
Houston, TX
I had a similar problem. Are you working with USA gallons or Imperial gallons? I Googled my spa to find the Liters spec to end the confusion

That's a good point. I always forget that an imperial gallon is even a thing. Either way, the company is based out of TN, and I'm from TN, and I'm pretty 99% positive nobody in Tennessee uses an imperial gallon... That being said, I'm going to get a fill meter for my hose and just measure it next time I fill the tub.
 
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