PH/TA both low, which to raise first?

[rubicon]

Upon fresh fill these are my readings:

Gallons 425
CH: 130ppm
TA: 60ppm (target 90ppm)
PH: 7.0ppm (target 7.6ppm)

I am going to leave CH alone but was wondering if I should raise PH first (sodium carbonate)? I know this will also raise TA and then I could adjust TA as necessary. Or should I raise TA first with Sodium Hydrogen Carbonate and then see where the PH is?

 

[Richard320]

TA has a wide range that's allowed. Just fix pH and TA will be fine. Looks like 4 tsp of Soda ash will push pH to 7.4 and TA to 72.

 

[pooldv]

Yep, just keep PH between 7.2 and 7.8 and you will be good.

 

[rubicon]

Thanks for the replies

Don't I also need to worry about the CSI number? With a PH of 7.4, TA at 72, CH 130 and temp at 100 the CSI is -0.28 which I thought wasn't good.

 

[Richard320]

Thanks for the replies

Don't I also need to worry about the CSI number? With a PH of 7.4, TA at 72, CH 130 and temp at 100 the CSI is -0.28 which I thought wasn't good.

Not at all. That CSI is still okay for plaster pools. Your spa isn't plaster anyway, so there's no danger at all of leaching Calcium from the surface.

Low CH might make it foam up more than you like, but you'll never need to worry about scale formation.

 

[rubicon]

Using the pool calculator it tells me I need 0.9oz of soda ash which seems to be more than the 4 tsp you recommended. Am I miscalculating?

 

[chem geek]

You aren't miscalculating. Richard said that 4 teaspoons (0.666... ounces) would get you to a pH of 7.4 and a TA of 72. If you put in 7.4 for your goal pH then PoolMath says 0.7 ounces which is what Richard said. The pH Up also increases TA by 11 ppm (you can see this in the "Effect of adding chemicals". Your goals were different than what he wrote.

Why do you want to target 90 ppm TA in a spa anyway? That's usually too high. Usually with aeration from spa jets, the pH rises and you may just try that to get your pH up without changing the TA. The only reason you'd want your TA higher was if you were going to be using a net acidic source of chlorine. Are you using Dichlor or are you planning to switch to using bleach after building up some CYA in the water?

 

[rubicon]

Ah, I was looking at the "by weight" not "by volume" since I was weighing the chemicals.

I thought I needed to increase TA to make the CSI number good. I am using Bromine. It sounds like I can leave it where it is and my PH should hold steady?

 

[chem geek]

You'll have to see to know. Just let the TA settle in such that the pH is relatively stable. If you were to use something acidic to create more bromine such as using non-chlorine shock (MPS) then you'd need a higher TA. Dichlor is also net acidic, just not as much. Bleach would be close to pH neutral, but pH would then rise from carbon dioxide outgassing so a lower TA would be needed.

 

[rubicon]

My PH continues to rise to 8.0 consistently after I bring it down to 7.4-7.6. The TA is now at 50ppm. I am only using bleach as my activator.

How can I get to a more stable PH?

 

[Patrick_B]

We are in the same boat, and I'm not sure if there is much. Some people have success with Borates for stabilizing pH, but I'm not sure it would help us. My makeup water is 8.3 so it's a fight. I have very high CH, so I've crushed my TA and it's about there now. Still, I'm adding acid once a week or maybe twice depending on makeup needs.

 

[chem geek]

For a spa, which is what I assume you are talking about given that this is the Spas and Hot Tubs forum, you not only need to have the TA no higher than 50 ppm, but you also need to target the pH at 7.7 to 7.8 -- don't lower it below 7.5 -- and also need to use 50 ppm Borates. For spas with aeration from jets and other sources, this is not optional. You can increase your borates using boric acid from Duda Diesel or The Chemistry Store. I also assume your spa is covered most of the time so that you do not have a lot of evaporation and refill.

 

[rubicon]

My PH has been holding at 7.4 now and my TA has dropped to 30. Is this acceptable?

 

[chem geek]

If you've got 50 ppm Borates and you make sure you don't add any net acidic chemicals to the spa, then you can have the TA be 30 ppm. I'd check it on occasion to be sure it's stable. I think you'd be better off having the TA at 40 ppm and having the stable pH be higher even if that's 7.8. A higher pH reduces metal corrosion rates and the extra TA gives you a little more cushion if any acidic chemicals are added to the spa.

 

[rubicon]

I don't have any Borates in there on this fill but the only thing I add is bleach and bromine tablets.

 

[chem geek]

OK then unless and until you get borates in the water, be careful with such a low TA level. Measure it regularly enough for you to know that it's not dropping further. Bromine tabs in theory do drop in pH over time as the bromine is used/consumed. They don't result in an acid as Trichlor does with CYA, but the bromine they produce still results in acid (hydrobromic acid) when the bromine is used/consumed.

 

[rubicon]

I ordered some boric acid. Looks like I will need about a pound for my 425 gallon tub.

I believe you are recommending I bring my TA up to 40 and my PH to 7.7-7.8 before adding the acid.

 

[chem geek]

Yes, at least to start and see how things go.

 

[rubicon]

I brought TA up to 40 and PH to 7.8 then added about 16oz of Boric Acid. About 12 hours later and my TA is still at 40 and my PH is 7.5.

Based on your feedback I think these are good numbers to stick with. I am hoping with the boric acid that both my TA and PH stay steady.

 

[chem geek]

It will help, but aeration of spa jets will drive out carbon dioxide that makes the pH rise. When you then add acid to lower the pH, the TA gets lowered as well. The borates don't stop this process but they slow down the rate of pH rise so you don't have to add the acid as frequently. It's the lower TA and a higher pH target that reduce the rate of carbon dioxide outgassing itself. See this chart for how over-carbonate water is with respect to air at various TA and pH.