pH and total alkalinity are important water chemistry factors that are often confused and misunderstood. This episode explains in detail what each of them are, what they do, and how they interact with other pool chemistry. Since pH impacts just about every other chemistry in water, it is important to manage it properly, according to the physics of water. Too often, pool owners and operators try to control pH, but it is a futile, costly effort. https://www.orendatech.com Show-Notes: [01:32] What is ph? [02:30] pH is an equilibrium [07:58] Negative logarithm of hydrogen [08:43] Let's not try to control pH. Physics is going to raise the pH in swimming pools. [09:50] Henry's Law of the Solubility of Gases [12:23] Buy a ph probe to find out your exact ph. [12:37] Your ph can raise from algae, vanishing edge pools, spas, spillover, or salt cell. [17:17] ph is the most impactful factor to the Langelier Saturation Index [18:53] Problems occur when ph lowers the LSI and water is starving for calcium [21:16] What is Alkalinity? [27:38] Adjusting alkalinity
00:00 - Intro
01:32 - What is pH?
02:30 - pH is an equilibrium
07-58 - Negative logarithm of Hydrogen
08:43 - Let's not try to control pH. Physics is going to raise the pH in swimming pools.
09:50 - Henry's Law of the Solubility of Gases
12:23 - Buy a pH probe to find out your exact pH.
12:37 - Your pH can raise from algae, vanishing edge pools, spas, spillover, or salt cell.
18:53 - Problems occur when pH lowers the LSI and water is starving for calcium
21:16 - What is Alkalinity?
27:38 - Adjusting alkalinity
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[00:00:00] Eric Knight: Hey, everyone. In today's episode, we are going to be discussing pH and alkalinity... two very important water chemistry factors that are tested, but not necessarily understood. So this episode is going to be describing what they are, how they work, how they interact with each other, because they are related.
[00:00:24] But they're different, and they get confusing, because, you know, if you have a pH over seven, which is neutral, that's called basic or alkaline and alkaline sounds a lot like alkalinity. They're not necessarily the same thing. So buckle up, because we're going to get into some chemistry here. I'm going to try to simplify it as much as possible.
[00:00:45] And that's what this show is all about. So thank you for listening and welcome to rule your pool.
[00:00:56] Welcome to Rule Your Pool. The podcast by Orenda that explains and simplifies pool chemistry so that anybody, regardless of experience, can understand it. I'm your host, Eric Knight, bringing clarity to these subjects so that you can bring clarity to your water. If you're ready to rule your pool, but let's go.
[00:01:18] So I've got this coin here and, uh, just to show how professional and official I am, I've got... we'll say tails is alkalinity, and heads is pH. It is heads. We're going to start with pH. pH stands for the power of Hydrogen, or if you want to be fancy, potenz Hydrogen, that is potenz, with a Z on the end. And basically what it is is a scale from zero to 14 that tells you how acidic or basic or alkaline a substance is.
[00:01:54] So zero to 14, seven, right in the middle is perfectly neutral. So perfectly neutral water has a 7.0 pH. As you go down, you move that decimal point and you go from seven to six. Now you have 10 times more acidity. Now we want swimming pools, typically between 7.4 and 7.6. Most textbooks would say that's the ideal, but anybody who's managed a swimming pool knows it's impossible to keep it there without chemical automation.
[00:02:25] And to be honest, even with chemical automation, it takes a lot of acid because pH naturally rises. All of these chemicals that we use impact the pH of the pool. And what that tells us is the pH is a reactionary chemistry. It moves. It fluctuates. And that's because pH is an equilibrium.
[00:02:46] It's an equilibrium. If you think of H2O, water, the molecule looks like Mickey Mouse. You've got a big oxygen and you've got two hydrogens on it. Kind of like Mickey Mouse's ears. And the lower the pH, the more the attached hydrogen stay. But as the pH goes up, one of those ears breaks apart and you're left with a Hydrogen that has broken apart.
[00:03:11] And an (OH-) which now has a negative valence, which is called a hydroxide. (OH-). The more hydroxide by percentage, the higher your pH. And because this is a logarithmic scale, it means that every whole number on this 0-14 scale is 10-times greater or less than the number around it. So, perfectly neutral water is 7.0.
[00:03:37] That means it's in equilibrium. 50% is going to be hydroxide. 50% is going to be separated Hydrogen. Okay. Awesome. Perfectly neutral. As you go down, from seven to six, now you have 10-times more acidity. Meaning Hydrogen is reattaching, and the power of Hydrogen actually increases, which is confusing because pH is a negative logarithm of Hydrogen.
[00:04:05] But read the blog. You'll see the graph in the charts it'll make more sense. So six is 10 times more acidic than seven. So five is 10 times more acidic than six, but it's a hundred times more acidic than seven, 10 times 10. This is starting to get out of hand. So four is a thousand times more acidic. Three? 10,000 times.
[00:04:30] So if we think about a chlorine like Trichlor, a very common three inch tab, stabilized chlorine, very popular in pool retail stores it's even popular in the trade. Trichlor has a pH of about 2.8. Well, that is between 10,000 and 12,000 times more acidic than neutral water. This is the main reason that putting trichlor in a skimmer basket is a big problem.
[00:04:56] That kind of pH, 10,000 times more acidic than neutral water, can damage your heater. It can damage your pump impeller. It can damage, you know, tear through a salt cell. If you had a salt cell, I don't know why you'd be putting trichlor in there, but hey, we've seen it. Okay. Orenda never gets called to the good pools, but it's not uncommon for a salt pool to supplement their chlorine with trichlor, I get it.
[00:05:21] But the pH correction chemicals that are used are often pretty extreme. Like muriatic acid is less than one on this logarithmic scale. Less than one is over a million times more acidic than neutral water. And then on the converse side, sodium bicarb? Oh, that's slightly over seven. I mean it's 8.3 to 8.6.
[00:05:41] Let's say 13 to 16 times more basic than neutral water. Not a big deal. But soda ash, which is sodium carbonate, very similar product, similar price, also raises the pH. That's 1200 times more basic than bicarb. They are not the same chemical, and you'd be astounded at how many professionals in this industry actually think they're the same thing, or they're very similar.
[00:06:06] They're not. I mean, they do a similar thing, but 1200 times concentration difference here. So what takes teaspoons of soda ash could take pounds of sodium bicarb.
[00:06:18] Liquid chlorine has an extremely high pH: 13. Okay. 13 is a million times more alkaline or basic than neutral water. So to correct for that, it's a habit in the industry that you have to put in a certain amount of muriatic acid to offset that high pH. In reality, you don't actually have to do that. Or at least not as much. Because once chlorine oxidizes and sanitizes, it actually releases some hydrochloric acid itself. And the pH is almost a wash. I mean, it's a slight rise, but it's almost a wash. But yet people put acid in because it, this temporary pH spike from the chlorine.
[00:07:04] And, you know, we are an industry of habits. I get it. So if anything, if you are going to do acid, you don't need nearly as much as you might think. I've heard of people doing a full quart of acid for every gallon of liquid chlorine. And you probably need like a fourth of that, but I'm not here to give advice on those. Consult a pool professional who doses chlorine.
[00:07:23] We are a specialty chemical company. We don't make any chlorine. We don't make any acid. So we're not making any recommendations on that, but you can follow the Orenda app. It's a free app. You can download it. That will give you very, very specific dosing instructions. So anyways, pH: negative logarithm of Hydrogen.
[00:07:44] Okay. So it bounces, it moves. It's very hard to nail down. So when you put in something like acid, it changes the pH pretty rapidly. Now granted, a small amount of acid in a 20,000 gallon pool. That's not a huge thing cause it's diluting so much. But if you did that in a bucket, the pH of that bucket tanks out with just a few drops of acid.
[00:08:07] So you've got to be careful, because acid is the most abused substance in the swimming pool business, hands down. I mean, we at Orenda have a philosophy of minimalism because we know that so many swimming pools are just chronically over-treated. They have way too many chemicals in them, and it's really, really difficult to keep water in balance when you constantly tweak it. Instead, here's an alternative. Use physics to your advantage.
[00:08:37] Let's not try to control pH. You're never going to win that battle. It's futile. It's always going to evade you like a rabbit in an open field. Good luck catching that rabbit. Instead. I want you to imagine putting that rabbit in a bedroom. Let it run around all at once, it's contained. Physics is going to raise the pH because pH in swimming pools, or in any water actually, is largely determined by the amount of carbon dioxide that's in the water.
[00:09:05] And you're thinking, "man, carbon dioxide, what does that have to do with Hydrogen?" Well, we didn't know either, but it's actually very important because of alkalinity. These two are very interrelated, even though they are different concepts. So the amount of carbon dioxide in your water is what determines what the pH of your pool is going to be.
[00:09:27] A lot of people don't know that. And to be honest, neither did we, we learned it recently. Physics tells us that the amount of CO2 in your pool is going to try to equalize with the air above the pool. This is called Henry's Law of the solubility of gases. You can look it up. Henry's Law. So in other words, if you've got a certain high percentage of CO2, but the atmosphere above the pool, that we all share, is a lower percentage, the pool is going to donate CO2. It's going to equalize. It's going to get rid of CO2 aerate it out until it is in equilibrium with the air above it. Then CO2 has no reason to leave the water and it kind of stays there.
[00:10:11] Now there's a few schools of thought on this. We were taught at first, when we learned this Henry's Law concept, that it goes up to 8.2 pH. And the truth is, it goes up to about 8.2 pH.
[00:10:25] It really has to do with your carbonate alkalinity level. And so we've got this chart that shows the higher your carbonate alkalinity, the higher that ceiling is. But whatever the ceiling is, roundabout 8.2, maybe it's 8.27, maybe it's 8.16. Whatever that ceiling is, pH cannot naturally rise over that number unless it's forced.
[00:10:50] And that's a key to think about. This is a hard stop. It's a ceiling. When CO2 equalizes with the air above it, the pH does not rise anymore, naturally. Use that information to your advantage. You're doing nothing wrong by letting the pH go up, or when you come back, even if you didn't intend to, you come back after three days.
[00:11:14] "Oh, my pH is so much higher. I need to hit it with more acid." Not necessarily. In fact, you probably don't. The pH is supposed to go up. You're not doing anything wrong. It's going to go up to its ceiling based on your carbonate alkalinity level. So when it gets there, if it ever goes over that ceiling, you know it was forced. Maybe by over-correcting with too much acid, and it etched your surface and pulled out a very high-pH calcium hydroxide.
[00:11:40] Remember that word earlier, hydroxide? That (OH-)? Super high pH stuff. Calcium hydroxide has a pH of 12.6. That's a pretty high number. That's 160,000 times more basic than neutral water. You pull that stuff out of your wall, you're going to spike that pH over 8.2. It could be nine. I've seen it as high as 10.
[00:12:05] Most pool test kits don't test pH that go over eight or 8.5 at the highest, but you can get a pH probe. They're not that expensive. You can buy them online. I did. And they go much higher. You just dip that thing in the water. It tells you in a second. It's pretty cool. It'll tell you exactly what that pH is.
[00:12:25] Another thing that can rise your pH a lot is algae. Algae consumes carbon dioxide. It takes it out of solution. It puts it in its cell wall. Well to the pool, that's no different than it offgassing. So if the CO2 is out of solution, boom, pH goes up. If you have a vanishing edge or a spa that spills over, or you have aeration, you've got these big jets in your spa, pH is going to rise faster in that pool.
[00:12:51] Same with a salt cell. That's going to raise the pH too, but it's not going to get over its natural ceiling. So let's use this as a containment strategy.
[00:13:02] If you don't over-correct with acid, you can determine what the floor is. Say you want to go to 7.5 every week. 7.5 is a great pH. It's going to rise up to a maximum of 8.2 or thereabouts. Okay. Let it. It's not necessarily going to get all the way to the finish line, because the closer it gets to its destination, the slower it rises.
[00:13:25] It's not going to get up to 8.2 immediately, unless it's forced. So if you use a high pH chlorine, if you use a salt cell, if you have aeration, you have this vanishing edge, you've got, if you have algae, you know, those will raise your pH faster because it's a faster mechanism of losing carbon dioxide. And that's really the name of the game.
[00:13:46] I mean, it's, it's about carbon dioxide in the water. So to lower your pH, you can either inject carbon dioxide as a lot of commercial swimming pools do. Or you put acid in the pool, which converts to carbonic acid, which is aqueous carbon dioxide. So we're going to have a little bit of a hybrid in here where the pH will determine the type of alkalinity you have again, because of how hydrogen interacts.
[00:14:17] The lower your pH, the more hydrogen is attached. The higher your pH, hydrogens break off. So you go from carbonic acid... once you get past 4.3, you get a species of alkalinity called bicarbonate (HCO3-). And then once you get over 8.2, a new species comes around and that's carbonate alkalinity. That's just (CO3--). The hydrogen's gone.
[00:14:41] Carbonate alkalinity is pretty attracted to calcium. So if you've ever thrown soda ash into a pool and it clouds up, there's a reason for that. The pH of soda ash is 11 something, and right there, you've converted bicarbonate alkalinity, because you rose the pH, into carbonate alkalinity. Let alone the fact that sodium carbonate, soda ash, is pure carbonate alkalinity.
[00:15:07] So you put that in there. Well, it's going to seek calcium. (Ca++) is looking for (CO3--). And you get calcium carbonate, which is the same substance as scale. And we'll have a whole nother set of episodes on calcium carbonate and the LSI, but basically it's precipitating because of the swing in pH so fast.
[00:15:30] The role of pH in water chemistry is basically that it controls, maybe not controls, but it at least influences just about everything else. One exception to this is in outdoor pools that use cyanuric acid. Without cyanuric acid stabilizer, pH controls the strength of the chlorine because the strong, bad-ass chlorine (HOCl) hypochlorous acid. When that pH goes up, the hydrogen breaks away and you're left with this much weaker, much, much weaker hypochlorite ion, which is an (OCl-).
[00:16:07] (OCl-). Well, both show up on your free chlorine test kit. But that hydrogen leaving means it has a lot less killing power. So without stabilizer, pH was directly determining the strength of your chlorine. And that's pretty significant because if your pH went up, you know, from, I think it's 50/50, right around 7.5, 50% strong, 50% weak.
[00:16:34] Well, at 7.4, you had a majority of hypochlorous acid. But at 7.8, it was starting to get pretty weak. At 8.0, you had almost no chlorine strength. But in an outdoor pool, that goes out the window because of cyanuric acid. We will have another episode on that. But pH does matter. It actually interacts with just about everything.
[00:16:55] Like I said earlier, it controls the species of your alkalinity, and we haven't even flipped to the other side of the coin to talk about alkalinity yet. pH is the driving factor. It is definitely the most impactful factor to the Langelier saturation index, the LSI. And the LSI is the objective measure of water balance.
[00:17:16] If pH moves, the LSI moves. So it really does matter where you keep your pH, but if you build an LSI strategy around this containment of pH, managing pH becomes much easier because it's very predictable. You know, it's rising. It's going to rise at the exact same rate every week, unless you add different chemicals or something else happens. Physics will move at the same speed.
[00:17:42] Use that to your advantage. You set the floor based on dosing properly and measuring the amount of acid you put in. Pre-diluting it, don't let it etch. Don't put acid straight in the pool to go straight to the bottom. We'll have another episode about that too. When you lower your pH to say 7.5 or 7.6, it will move up.
[00:18:04] And then, after a week, put it back down. It'll move up again, put it back down. Don't fight it. Don't keep nitpicking at pH because the more you put in, you're going to have to replace more alkalinity. Now you put bicarb in, now you're bouncing. And this pH will evade you. And you're gonna spend a lot on chemicals that you did not need to spend.
[00:18:27] In reality, pH is very predictable, but it's very frustrating when you're fighting it. You'll never win that battle. So we have to understand and embrace the physics of it. Cause I don't care how good you are. Nobody's good enough to beat physics. Okay.
[00:18:43] If you Google this, pH, mainly because it is the driving factor of the saturation index, the LSI, pH is associated with things like destroying heaters. You know, ripping the copper out of heat exchangers and scaling up salt cells if it goes too high. And causing all these etching problems and fading liners. Well, in reality, yes, that is pH, but it's not because it's a low pH. It's a problem because that low pH lowers the LSI, and the water becomes starving for calcium.
[00:19:18] So if you have a floater full of three-inch trichlor tabs, the immediate vicinity around that floater has a very low pH. Which means it has a very low LSI. So if that floater, say you have a vinyl liner pool, or a fiberglass pool, if that floater is near the wall, that spot where that floater hangs out is going to get destroyed.
[00:19:39] If it floats over a step, that step is going to get destroyed. Not because chlorine did it, but because the pH of trichlor is so low, 10,000-12,000 times more acidic than water, it's going to damage it. It lowered the LSI. It changed it right there. That's pretty significant. So when pH gets out of whack, i.e. when you fight it or you mismanage it, there are serious consequences. So pH absolutely matters.
[00:20:10] But as a recap, it's an equilibrium of hydroxides and hydrogen. And the higher it goes, the more hydrogen likes to break away. And the lower it goes, the more hydrogen likes to come back. If your pH gets too high, your LSI will get very high. Calcium will start to precipitate like scale or dust of other kinds. Or if you get too low, Your LSI will be low. It will be starving for calcium, and it's going to be looking for it. This is when you get etching. This is when you get discolorations of plaster surfaces, pigment loss, in a vinyl liner. Destroyed heaters. Those kinds of things. So let's shift over to alkalinity now.
[00:20:52] When I first started researching alkalinity online, years ago, I was astounded at how little information there actually was online, in the pool business anyway. And I had to look at other industries to find out and learn what it actually is. And what that told me was this is a highly-googled question. Most people don't understand this, and I felt really good about that because I didn't, you know, I didn't know.
[00:21:20] If people are Googling this, chances are, it's one of those topics that you're supposed to know, but you don't want to admit you don't know. There's nothing to be ashamed of, guys. If you're listening to this and you don't really understand alkalinity, you're not alone. It's like everybody. And I was included in that too.
[00:21:36] And the only reason I'm not anymore is because of the exhaustive reading and talking to much smarter people to really kind of comprehend what it is. Alkalinity is a measurement of how much. It's in parts per million. How much dissolved alkali is in your water. Total alkalinity is every type of alkalinity added up in one measurement.
[00:22:04] Now there's, there's three main types, but there's really two types that we primarily deal with in swimming pools. And that's bicarbonate and carbonate alkalinity. So the higher your pH, if you get over 8.2, bicarbonate starts converting into carbonate, because the hydrogen leaves. Bicarbonate being (HCO3-) over 8.2, between 8.2 and 8.3, those hydrogens begin to break away.
[00:22:32] And the higher your pH goes, the higher that equilibrium of carbonate alkalinity becomes. But there's also other types of alkalinity. Like when cyanuric acid is in the water, you get cyanurate alkalinity. Basically alkalinity is something in the water that has the ability to accept or reject a hydrogen. So it can either receive more hydrogens to it, or it can donate them back. That means it's a buffer. It has the ability to buffer your pH. This is the relationship.
[00:23:04] If you have a lot of alkalinity, the textbook recommends 80 to 120, let's say you have 120. It's going to be pretty hard for you to lower your pH too far.
[00:23:16] Because the acid that you put in the pool is going to have to neutralize out that alkalinity. Yeah, you'll lower the pH, but you're not going to be able to tank the pH, because you have a lot of insulating buffering capacity that the acid is going to get neutralized on in the process of lowering that pH.
[00:23:33] Now it doesn't necessarily stop it from going higher. Because the higher your carbonate alkalinity, the higher that natural ceiling of pH is actually going to be, whether it's 8.2 or 8.27, or 8.31, or whatever it is, it's not really stopping you from going high. Physics itself will, because like we said, in the last segment here, Henry's Law, once carbon dioxide equalizes with the air, it has no reason to rise. So carbon dioxide stays in the water. Unless it's forced.
[00:24:05] So it's really a buffer from pH going too low. So you don't necessarily want a super high level of alkalinity, but you definitely need some. Some people would think, "oh, I need a lot more alkalinity." Well, maybe if you're using trichlor only, which we don't recommend at Orenda anyway, because of over-stabilization reasons.
[00:24:24] But let's say you are using trichlor only. That low pH is constantly taking out some alkalinity. It's just how it's going to happen because it's an acid. Okay. Yeah, you need more alkalinity in a pool like that. Maybe you need 100-120. I'm not here to prescribe exact range chemistry because if you know anything about Orenda, we don't really prescribe to range chemistry anyway. We're more of an LSI-based philosophy. But you would need more alkalinity in an acidic type of chlorine. Back in the day, they used to use gas chlorine, and that was really acidic. So you absolutely needed more alkalinity to handle that kind of chlorine. But nowadays, non-stabilized chlorines, they're alkaline. They're basic. Cal hypo has a pH around 10.8.
[00:25:12] Liquid chlorine is 13 something. Salt puts out a high pH byproduct, even though it creates pure chlorine. So most chlorines that are used in swimming pools now are basic. You don't need as much alkalinity for that. What matters here is the LSI balance. But if you think about it, this buffering capacity, it matters a lot because the relationship of hydrogen leaving or binding to it, if it can get in the way of that, it means that your fluctuation of pH is not going to be nearly as much.
[00:25:49] You're not going to have these major swings cause, oh my God. If you, if you could drop your pH to four really easily. Like with a gallon of acid or something like that, you would destroy your pool really rapidly. And then it could swing way back up and then you'd get scale. And I'm not to say that you can't have etching and scale in the same location. We see it all the time, but it's a localized event and it's not systemic to the entire pool.
[00:26:17] If you drop acid in a column and it goes straight to the bottom, because acid is denser than water, it just punches right to the bottom. Yeah. You're going to etch. And you're going to have a lighter spot there because it took out some pigment when it took that cement out. And then the cement, specifically the calcium hydroxide in it, has a very high pH. Boom. Now you have another LSI violation and you get scale next to the etching. It happens. I know it sounds counterintuitive, but it all boils down to overcorrection. So we want to avoid those overcorrections and total alkalinity helps with that.
[00:26:50] It helps as a buffer and that's its primary role. So total alkalinity measures bicarbonate plus carbonate, plus hydroxides, plus cyanuric acid or cyanurate alkalinity, I should say. I think borate has some alkalinity value. Whatever accepts or rejects hydrogen can be considered in this buffering capacity of the water.
[00:27:09] So let's talk about how you actually adjust alkalinity. Because it's about how much, it's not necessarily about the strength of what you're using. It's literally a parts per million. So sodium bicarb, even though it's 1200 times weaker than soda ash, in terms of pH, it actually adds a lot of alkalinity because it takes a lot more bicarb to do the same pH correction than it does that one scoop of soda ash. So you get a lot more parts per million of alkalinity. Yes, it's bicarbonate, but that's a good thing. Bicarbonate alkalinity is the dominant species in the pH ranges that we want our swimming pools to be in. So that's why we use sodium bicarb to adjust alkalinity.
[00:27:54] To remove alkalinity, i.e., burn it off or lower it, use acid.
[00:28:00] So pH is on a logarithmic scale. It's an equilibrium of hydrogens and hydroxides. It will move very rapidly, but if it is contained, instead of trying to be controlled, you could get it into a pattern where you set it to 7.5 or 7.6, and it will naturally rise up at the same pace until it eventually hits its ceiling, which is about 8.2.
[00:28:25] But because of the way that it rises naturally, it's going to slow down dramatically and it may never actually get to 8.2. You can just lower it right back to 7.6. This is a fraction of the amount of acid that most people would use. Because most people fight pH. And then they have to bring up their alkalinity cause they used too much acid and it neutralized too much alkalinity.
[00:28:47] We had Orenda, we're proactive. We don't want to do that. We want to actually follow the physics of a swimming pool. And that was the point of this episode. Alkalinity is just the buffering capacity that helps insulate the pH, for lack of a better term. You've got to get through that alkalinity.
[00:29:03] It's like, um, parents or a body guard, maybe, you know. It's like, "Hey, you want to pick on that pH? You've got to get through me first." And so you've got to neutralize alkalinity to make a bigger change on pH. These are two very complex, I should say concepts, but just remember pH is an equilibrium that fluctuates. And alkalinity is the insulating buffering capacity measured in parts per million.
[00:29:32] There's a lot more that we're going to cover on this. Both are very important to the saturation index, or water balance. Both are very interconnected with a lot of other chemistries: cyanuric acid, chlorination, all these other things. So we will cover those in more in the rest of our episodes, but thank you for your time.
[00:29:52] And I hope you got some value out of this.
[00:29:54] Thank you for listening to rule your pool. A podcast by Orenda technologies. For more information on what we discussed in this week's episode, check the links in the description or visit www.orendatech.com. I hope you find this show valuable enough that you tap that subscribe button and share it with your friends.
[00:30:16] You can also like us on Facebook and social media. With our help, you'll be able to rule your pool without over-treating it with chemicals and wasting money. I'll see you next episode.