A pool store printout shows "adjusted alkalinity", but presented as if it's the "real" alkalinity. It is only used for LSI and pH ceiling calculations, not acid dosing. Acid doses are based on TOTAL alkalinity, because cyanurate and borate contribute to the TA, and acid will neutralize on them too.
00:00] - Intro
[00:36] - Adjusted Alkalinity on a Pool Store Printout
[01:34] - Adjusted Alkalinity = Carbonate Alkalinity
[03:10] - Cyanurate and Borate also contribute to Total Alkalinity
[04:42] - Increasing CYA increases TA. About 1/3 of CYA is Cyanurate Alkalinity
[06:14] - Is Adjusted Alkalinity the "Real" Alkalinity?
[07:37] - One Breath Summary
182. Understanding Adjusted Alkalinity
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Eric Knight: Hey everybody. Welcome back to the Rule Your Pool podcast. This is episode 182, and it's just me, your host, Eric Knight. And I'm going to be short on this one because it's not that complex of a topic, we're going to get through it quickly because I got a call this past week asking a question that reminded me of something that I had in the queue years ago, when I was still with Orenda, and we just never got to it.
So it's a great excuse for me to go to a blast in the past. Get back to that topic and talk about it on this show for you. So without further ado, let's talk about adjusted alkalinity and what it's actually used for.
[00:00:36] Adjusted Alkalinity on a Pool Store Printout
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Eric Knight: So I got this call from somebody that I've known quite a bit in this industry, and he was talking about pool store readouts. Now, I have been an open critic in the past of how some of these pool store softwares will just give recommendations, sort of siloed. Like, oh, your pH is off, so do this. Sometimes it's selling soda ash to raise the pH, even though you and I know it's going to naturally rise, but that's not the point. You know, just fix the pH. And then here's something for alkalinity, fix that. Without any regard to what it'll do to the pH. Okay. And then you've got calcium, you got to fix that. And everything was based on range chemistry.
[00:01:34] Adjusted Alkalinity = Carbonate Alkalinity
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Eric Knight: But in this case, this pool store, I'm not going to name names because it's not my business. But this pool store said adjusted alkalinity on there. And that got him thinking, and so he reached out to me, said, Hey, wait a second. What is adjusted alkalinity supposed to be used for? Is it supposed to be used for acid dosing?
And I realized this is worth talking about because I used to get this question quite a bit. Of course, at Orenda, we talked about carbonate alkalinity. By the way, adjusted alkalinity is just another way of saying carbonate alkalinity. In other words, just bicarbonate and carbonate ions. And if your pH is below 8.3, it's pretty much just bicarbonate ions. So that's what adjusted alkalinity is.
And um, anyway, it's, it's on the test results. It's on the piece of paper that they print out that your adjusted alkalinity is this. And then it starts making dosing recommendations based on that. Well, that's a big problem. Because that's not how you dose acid. Let me explain why.
Adjusted alkalinity is not used for dosing. It is not the entirety of the buffering system. There are other things that contribute to total alkalinity. That's why when we get to carbonate alkalinity, it's called adjusted. You had to adjust from total alkalinity to get to carbonate alkalinity.
Let me put it this way: total alkalinity is the entire buffering capacity in the water. And it could be multiple systems. In most swimming pools, especially chlorinated ones, outdoor pools, are going to have at least two buffering systems within that total alkalinity. And that's going to be carbonate alkalinity, which is again, bicarbonate ions for the most part. And that's the bulk of your alkalinity.
[00:03:10] Cyanurate and Borate also contribute to Total Alkalinity
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Eric Knight: But you're also going to have cyanurate alkalinity, because we have CYA in the water. And if we have CYA or cyanuric acid, that contributes to alkalinity too. We know that because to get to carbonate alkalinity when we're calculating the LSI, we have to know our CYA level. And the CYA needs to be deducted from total. But think about that for a second. If it needs to be deducted from total, that means it's part of total, right? And if we're adding acid to the pool, it's not like acid says, I am only going to neutralize bicarbonate ions. Acid doesn't do that. Acid is going to neutralize on whatever alkalinity is in there, including cyanurate ions. So when you do an acid dose, you're basing it on the total alkalinity.
By the way, if you use borate, this contributes to that as well. Although borates, they don't take hydrogens like, um, cyanurate and bicarbonate do. It takes a hydroxide. So it's actually a better buffer against a rise in pH. We have a whole episode on that as well. But it does contribute to your total alkalinity. Now, the Orenda Calculator factors all this in for you. Just put your CYA in, put your borate in, and it's going to adjust the carbonate alkalinity. And you can see it for yourself. I remember when we decided, instead of just having it going on in the background, because a lot of people were asking us, well, is this adjusted alkalinity? Is this total? We just decided to display it. You know, in real time. So when you add CYA, you'll notice the carbonate alkalinity goes down, and when you increase borate, the carbonate alkalinity goes down because those are contributing to the total.
[00:04:42] Increasing CYA increases TA. About one third of CYA is Cyanurate Alkalinity
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Eric Knight: Now, if I just have a total alkalinity of 80, let's say. And I add a bunch of cyanuric acid, indeed that total alkalinity will increase. Yes, it will. So if you add CYA, and you come back the next week and it's slightly higher, don't be surprised. Because you added cyanurate alkalinity to it and it contributed to total alkalinity.
Now, if you test alkalinity first, total alkalinity. You find out that you have say too much, CYA. Let's say you have 60 parts per million cyanuric acid. The rule of thumb is you subtract roughly one third. So the rule of thumb is a third. It's not exactly that. It depends on the pH and stuff, but the calculator's precise. But let's just say it's a third. Take a third of your cyanuric acid and subtract from your total. So if I've got 60 cyanuric acid, a third of that is 20 parts per million. I take 20 parts per million away from my total alkalinity. And unless I'm using borate, that's going to be my carbonate alkalinity. You can see this in real time. Play around with the Orenda Calculator, you'll see it.
By the way, there's no way to test for adjusted alkalinity. It's in the name, you have to adjust for it. And that's a calculation just like the LSI. There's no reagent or test strip that can just tell you the LSI in one go. You have to test a bunch of different things and do the calculation and figure it out. It's no different here. So you're going to test total alkalinity, which is what you're going to base your acid dosing off of, and you need to test your cyanuric acid. And if you're using borate, you need to test for them. Then you can calculate the adjusted alkalinity.
[00:06:14] Is Adjusted Alkalinity the "Real" Alkalinity?
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Eric Knight: So back to the original question, why would the pool store readout say adjusted alkalinity? The inference here is saying that it's like the real alkalinity that you have. Not for dosing. It's the real alkalinity for the LSI calculation, and one other very important thing. The pH ceiling. So the adjusted alkalinity is really just going to tell you, or the carbonate alkalinity is really just telling you how carbonated your water is.
That's what the LSI cares about. So we plug that into the LSI formula. And that's how you determine your pH ceiling. That's how you determine how high your pH can naturally rise. The cyanurate and the borate, they don't affect the pH ceiling the same way. Now they do change the amount of carbonate alkalinity, because it's a deduction from total. But they're not contributing to that, if that makes sense. It's just a bigger subtraction factor from the total alkalinity that you tested.
So I hope this clears it up. I think I just made it worse probably. But, um, let's see if I can summarize it. Actually, I actually had a request from, uh, one of the listeners. I don't know if you remember this, but years ago I would try to summarize the entire episode in one breath. And I got pretty good at it, but I'm a lot older now and I have a child and I'm not sleeping as much, so we're going to give it a shot. Got a bit of a cold right now, so, ugh.
[00:07:37] One breath summary
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Eric Knight: There's no test for adjusted alkalinity. You have to test for total alkalinity, and that's going to be what you base your acid dose off because that's the entire buffering capacity of the water. So when you put acid in, it can't distinguish bicarbonate ions from cyanurate. It's just going to neutralize on everything.
So do not use the carbonate alkalinity or adjusted alkalinity as your acid dosing metric. It is only used for calculating the LSI and the pH ceiling because it tells you how carbonated your water is. And if you know how carbonated it is, you know how much CO2 there is to lose, which determines how high your pH can rise.
Nailed it. I'm back baby, episode 182 of the Rule Your Pool podcast. I hope you got a lot of value out of this.
Just so you know, we've got some classes coming out this year. We're going to be doing a regional tour. You can check it out at watershape.org/events. We are also going to be doing a bunch of live virtual classes and we got our education vacation going to be going on most likely in December. We don't have that scheduled yet, but it's going to be in Jacksonville, Florida. So stay tuned. Check out watershape.org. Join our email list so you can stay updated on it, and we hope to help you achieve mastery in whatever it is that you want to do in this industry. I'm Eric Knight. Thanks for listening.