After a brief overview explanation of pH, we discuss what raises pH, and what lowers pH. In short, it's about dissolved CO2 in your water.
00:00 - Introduction to our new seven-part series
00:30 - What is TDS?
02:39 - Myths about TDS
04:32 - What raises TDS?
06:29 - What lowers TDS?
07:05 - Reverse Osmosis filtration
07:34 - Summary
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95. 5/7 - What raises and lowers Total Dissolved Solids (TDS)?
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[00:00:00] Eric Knight: Welcome back everybody. This is episode 95 and part five of our seven part series on what raises and lowers given chemistry factors in a swimming pool. I'm your host, Eric Knight. This is The Rule Your Pool podcast, and in this episode we are going to talk about what raises and lowers total dissolved solids or TDS.
[00:00:19] If you want to learn more about TDS, we cover it in more detail in episodes 7, 18, 36 and 47. So let's get right into it.
What is TDS?
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[00:00:30] Eric Knight: Let's start by defining total dissolved solids or TDS. TDS is exactly what it sounds like. It's the sum of all dissolved solids in your water. This includes total alkalinity, total hardness, which is calcium hardness, and if you have magnesium, that would be included in that.
[00:01:12] And metals like iron, copper, and manganese if you have them. But although metals are in low levels. It also includes things like cyanuric acid and borate if you use them. Phosphates technically, but phosphates are such a small amount. They're measured in parts per billion that it's like a rounding error. You would never really notice it.
[00:01:31] But the main contributors are going to be those minerals, like total hardness and salts. So it's not just salt if you have a salt water pool, it's also byproducts of liquid chlorine and cal hypo and things like that. And one common myth that we hear about TDS is that it contributes directly to cloudy water or turbidity.
[00:01:51] That's technically not true because all these solids we're talking about, if they're going to be measured on TDS, they are dissolved. They're invisible. Now that said, if conditions cause some of these solids to come out of solution, , then they can start clouding the water. Like if you have a high LSI violation and you get calcium carbonate to come out of solution, then it'll cloud up your water. And that absolutely is true.
[00:02:17] But if it's technically fully dissolved, it should be invisible. It shouldn't have anything to do with turbidity. And another myth that we see about TDS actually comes from the textbooks. Yes, it's our opinion that it's a myth, but we've done a lot of research on this, and we have not found any evidence to suggest that the textbook parameters for TDS make any sense.
[00:02:39] What they say, depending on the book you read, you can't go over 1500 parts per million of TDS over your tap water. Well, boy, isn't that nebulous? What if you have really high TDS out of your tap? What if you have super high hardness and super high alkalinity out of your tap? Or well water with a lot of metals in it? It's still 1500 for you? As opposed to the city water that has almost nothing in it?
[00:03:06] That to us, seems somewhat ridiculous. So we did some research on it and we found that that's really just kind of an arbitrary number that was written in the swimming pool textbooks. There's no evidence to back it up. We've looked. We've asked. Haven't found any. In the research that we've done, they don't really care until it gets over about 12,000 parts per million.
[00:03:26] I've also seen sources that say about 6,000 parts per million. And a lot of that has to do with accuracy of testing and effectiveness of disinfection. Now, I'm reading this from multiple different sources. They don't all agree. I'm not going to pretend that there's unanimous consent on what TDS should be. I'm just relaying what's out there to you and simplifying it. But the idea that you can't go over 1500 parts per million over your tap water doesn't make sense.
[00:03:54] Now I want to be very clear about this. It does matter what in your TDS is high. So for instance, you may have a salt water pool with 3,600 salt and you know, 400 calcium and 60 alkalinity, and you're doing it the Orenda way. Everything's good, everything's awesome.
[00:04:15] But you have a hundred cyanuric acid for some reason. Okay? That's not the Orenda way. That cyanuric acid is the reason you would need to dilute your water. It's not the salt, it's not the calcium. It's not the alkalinity. It's the CYA.
What raises TDS?
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[00:04:32] Eric Knight: Okay, so let's get into this. What causes TDS to increase? Well, just about everything leaves behind some sort of dissolved solid, and hopefully it's not a harmful byproduct. That would fit our philosophy of not leaving something behind that you don't want long term. But the two major contributors to TDS are going to be salt and minerals.
[00:04:52] Salt, of course, you can add if you have a salt water pool, you add bags of salt, you dissolve it. Great. But salt is also added from chlorine, liquid chlorine in particular. One gallon of liquid chlorine in 10,000 gallons of water is going to leave behind about 17 parts per million of TDS. 15 of that is pure salt. So that's how salt actually climbs up in a liquid chlorine pool.
[00:05:17] It leaves it behind. That's not necessarily a bad thing, it's just something you need to be aware of. Over time, that will actually increase your conductivity and should help your chlorination be more effective. But that is up to a certain point. At some point, you get too much and you start to get diminishing returns.
[00:05:34] Cal hypo also leaves behind some TDS. It leaves behind four parts per million of calcium hardness per pound of Cal hypo in 10,000 gallons of water. It also leaves behind some salts. I don't know the exact amount. I couldn't find that when I was researching for this episode, but I'm sure it's out there somewhere.
[00:05:51] If you raise your total alkalinity, yes, your TDS also goes up. If you raise your calcium hardness, TDS goes up, et cetera. But these are all generally pretty small levels. Couple hundred here, 50 there, 10 or 20 here. It's not a major change to your TDS like salinity would be.
[00:06:11] TDS itself, just think of it kind of like the overarching sum of everything that is still in your water. And it's not a 911, it's just not. It depends on what is too high in that TDS to determine if you need to reduce it.
What lowers TDS?
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[00:06:29] Eric Knight: So how do we reduce it? What causes TDS to decrease? Well, if you want to lower TDS, you need to dilute water. And you need to replace that water with a lower TDS fill water. Whether that's your tap or rain and snow. That's pretty much it.
[00:06:47] We talked about in episode 93, if you really had to reduce calcium hardness, you could throw soda ash in there deliberately to precipitate calcium carbonate, and then you could vacuum that to waste. Technically that would also reduce your TDS, but it's kind of a pain to do. We don't recommend it.
Reverse Osmosis Filtration
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[00:07:05] Eric Knight: So just think dilution is the solution. Another way you could do that, and you know, going back to the previous episodes, I guess I forgot to mention this, you could do RO filtration, reverse osmosis filtration. That'll take just about everything out. TDS, cyanuric acid, calcium hardness, total alkalinity.
[00:07:23] I should have mentioned that in earlier episodes, but they're already done, people. They're already done. I can't go back now. We have to move forward as an audience. I'm sorry, I forgot reverse osmosis filtration. That is another way to do it.
Summary
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[00:07:34] Eric Knight: So in short, in summary, TDS is the grand sum total of everything dissolved in your water, and it does not contribute to water clarity issues unless those solids come out of solution.
[00:07:48] The main contributors are salts and minerals. If you want to raise it, put more stuff in your water. If you want to reduce it, dilute water. Pretty easy episode, huh? Less than 10 minutes. I'm feeling pretty good about this. This has been episode 95, part five of seven. Only two more to go. Thanks for sticking with us.
[00:08:07] I'm your host, Eric Knight. This is the Rule Your Pool podcast. If you have questions, reach out to us on our email podcast@orendatech.com, or visit our help center, ask.orendatech.com. Thanks for your time. See you next week.