Bob Lowry Explains the Cal Hypo Stain Mystery

A black stain shows up on the pool floor right after you add cal-hypo and your brain jumps straight to “drain it and acid wash.” We slow that moment down and explain what’s usually happening: copper that was already there, hiding as copper sulfate, getting oxidized by chlorine into black copper oxide. Once you understand that chemistry, you stop chasing the symptom and start fixing the cause. 

We also get practical about what actually works in pool stain removal and metal control. Ascorbic acid can lift a stain, but it doesn’t remove copper from the water, which is why stains can come roaring back after you chlorinate. We talk through the real role of sequestrants and chelating agents, why they break down from photodegradation and oxidizers like chlorine, non-chlorine shock, UV, ozone, and AOP, and why following the dosing label is the difference between control and repeat stains. If you want a longer-term solution, we cover metal removal options like Q-Lator setups and the blunt but effective drain-and-refill approach, plus better cal-hypo handling so it dissolves instead of sitting on the surface. 

Then we shift into two “easy to ignore” problems that turn expensive fast: algae and zero chlorine. Algae multiplies by cell division, builds a protective polysaccharide layer, and punishes anyone who waits a week to respond. And when a pool has no chlorine residual, the risk isn’t just cloudy water, it’s bather-to-bather disease transmission. You’ll even hear a simple post-swim warm shower tip to reduce exposure when you’re not sure about water quality. Subscribe, share this with a pool pro or homeowner, and leave a review if it helped you prevent the next stain or outbreak.

A bag of cal-hypo can “create” a black stain in seconds, but the real problem is usually hidden copper that oxidizes into black copper oxide. We break down how to remove metals for the long haul, why algae gets out of hand fast, and why a chlorine residual is the only real shield against bather-to-bather disease transmission.  
• copper sulfate stains hiding in blue water, then turning black when shocked  
• ascorbic acid lifting stains but leaving metals behind  
• sequestrants and chelating agents binding metals, then degrading from sunlight and oxidizers  
• removing metals with Q-Lator options or by draining and refilling  
• preventing cal-hypo from sitting on the pool floor by pre-dissolving and dispersing  
• algae multiplying fast, forming a polysaccharide shield, and why brushing matters  
• why swimming with zero chlorine raises disease risk and what a warm shower can do after  
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Transcript

Welcome And Coaching Invite

SPEAKER_01 1:02

Hey, welcome to the Pool Guy Podcast Show. In this episode, I have another best of Bob Lowry for you. And in this episode, we're going to talk about what happens when you put Cal Hypo in a pool and it develops a black stain. And Bob Lowry is going to go over the cause of that and some solutions for that. Are you a pool service pro looking to take your business to the next level? Join the Pool Guy Coaching Program. Get expert advice, business tips, exclusive content, and get direct support from me. I'm a 35-year veteran in the industry. Whether you're starting out or scaling up, I've got the tools to help you succeed. Learn more at swimming poollearning.com. Here's another what if a lot of people are using some kind of copper to kind of compensate for the chlorine shortage. You add a bag of cal hypo to the pool, and all of a sudden, pretty much instantly you notice a black stain on the bottom of the pool. Right. And, you know, what do you do in that situation and what causes that?

SPEAKER_00 1:58

Well, the first thing is it it probably scares you to death. Because you're, you know, what goes through your mind is, oh my God, I'm going to have to drain this pool and acid wash it for free, you know. But so don't be a don't be nervous about that. It's okay. There are some things you can do, but the reason that it happens is that there's already a stain on the bottom of the pool, and you didn't know it. And usually that the

Why Cal-Hypo Triggers Black Stains

SPEAKER_00 2:27

stain is copper, and it's copper sulfate, and it's kind of a blue color, the water's blue, and especially at a depth of three or six feet, it's hard to see that it's a little bit blue down there or blue-green, because the water's blue. So you can't see it, but when when the when the chlorine hits it, it actually the sulfate, because it has less energy or less potential, the oxygen from the chlorine makes its way into and gets rid of the sulfate, and you end up with copper oxide instead of copper sulfate. And copper oxide is black. The black is caused from copper being on the on the bottom of the pool. And just like you would take care of any stain, you can try to use ascorbic acid, which is one of the good ones for removing a stain, but it's not so good at keeping the stain from coming back. So understand about sequestering agents and chelating agents. They surround metal that's in the water and prevent it from combining with something else so it will precipitate or cause a stain. But the molecule itself is a man-made molecule and is subject to degradation from sunlight called photodegradation, and from chlorine just from it being oxidized, and from non-chlorine shock, or from UV or an ozone generator, or even AOP. Any of those things are oxidizers, and they will reduce the sequestering agent. When the sequestering agent is reduced, the metal is again free to combine with things and cause a stain. So these sequestering agents don't get rid of the metal. Even if you use ascorbic acid and you get the stain off the wall, the metal's still in the water, especially with ascorbic acid. As soon as you chlorinate, you wipe out the ascorbic acid and the and the metal is free again to go back to being a stain. So you need to get the metal out of the pool. There's only a couple of ways to do it. You can either use a thing called the Q-Lator or see your later, whichever way you want to pronounce it. But the Q-Lator in a bag or a little cage can remove it, but bear in mind that it may take a week or 10 days to get rid of it if you put something in the skimmer. You can use one of their prefilters, and as I said, use a separate pump and pump the water through one of their pre-filters and back into the pool, and within a few hours you can get the metal level down. But you need to understand that if you sequester it, you're going to need to keep adding sequestering agent. As it degrades, you need to replace it. And the bottle of the product that you have will tell you how often you need to put it in. And they may say you need to put it in once a week, once a month, once every two weeks, or whatever. It's not because they want you to keep using the product. They do want you to keep using it, but they want you to keep the metal from causing a stain. And they don't want to get a bad name. They don't want to say, well, you know, a customer used said, I used this product and stain came back in a week. You know, well, the stain came back because you didn't do what the label said and add it again next week. It's better to get rid of the metal if you can. The only other way to get rid of the metal, of course, is drain to drain some water and refill it.

SPEAKER_01 6:36

And also as a side note, I would tell that pool tech to stop using cal hypo in that pool just as a hedge there bet.

SPEAKER_00 6:42

Well, you

Remove Metals Or Stains Return

SPEAKER_00 6:43

know, what you may want to do is dissolve some of the cal hypo in a bucket of water and then disperse it around the pool evenly or in front of a return line or something so that it gets dissolved instead of falling to the bottom and hanging out on the on the bottom. That's probably not good for any pool. Yeah. To leave a chemical sitting on it for very long. Any chemical.

SPEAKER_01 7:09

Here's one. And this happens a lot with a lot of new pool techs. What if you see algae in the pool? It maybe a little bit on the step area, maybe a little bit in the deep end, but you really do nothing to treat it. You don't raise the chlorine up, you don't you may brush it, but you won't do anything like add an algae side. What would happen in a pool like that where you're kind of ignoring the algae problem the first week you see it?

SPEAKER_00 7:33

Well, understand that that algae it multiplies by cell division. So one becomes two, two becomes four, four becomes eight, eight becomes thirty-two, and so on. It means that one algae could actually become a million in about 60 hours. So if you have algae enough that you can actually see it, it could be almost a million times larger by the time you come back, if it's a week later. So and it would take a huge, a huge amount more of algacide or chlorine to kill it. Once you see algae, by the way, that means that it's dense enough that you can see it. If you looked at only a little bit of algae in the pool, you actually can't see it. So you may have algae growing on your pool right now and don't know it. But as soon as you see it, now you see it, by the time you see it, it's already colonized and mature. And it's starting to, once it colonizes and matures, it secretes a clear dome over itself called polysaccharide. And that saccharide is difficult for chlorine and other things to get through it. It's a protective mechanism. So it's difficult to get to get chlorine to go through that. And that's one of the reasons that we want to brush the pool. Even if there's nothing on what you think is nothing on the walls, brush the pool and you will break up that that polysaccharide and allow your chlorine to get into the uh algae that's growing on there that you can't see. You know, you either need to brush the pool or vacuum. And don't just keep vacuuming the pool. We need to, we need to brush it. And it should be brushed. If you're going to brush the pool, you brush it first and then and then vacuum. But many times you brush it and then vacuum. And that's a good business to get into. It keeps algae from from adhering to the walls, and it breaks up the slime layer once it does, once it starts to to grow.

SPEAKER_01 10:10

And that reminds me my son, my son likes to tell his friends this when he said, Would you rather me give you a million dollars or pay you one penny a day and double it for 30 days? And that's kind of like that algae how it multiplies, because if you get that one penny and double it every day for 30 days, it's more than getting a million dollars in payment. So he likes to kind of trick his friends with that little that little one there. And that reminds me of you know, a rookie mistake is not to treat the algae and and ignore it, or not to think it's a big deal because you come back the following week and it's a big deal by not treating it when you first see it.

SPEAKER_00 10:45

Yeah, and it is a big deal. And even though you can see it in one spot, it may be growing, it it may be spread out and growing in a lot of other spots. It just isn't it hasn't turned green yet.

SPEAKER_01 10:58

Here's what what if you swim in a pool and there's zero chlor chlorine in there, and this could happen at any stage where maybe you're not paying attention to the chlorine level if you're a homeowner and you're not checking your chlorine often. But what happens to a person who swims in a pool where there's no chlorine in the pool? Maybe they're in there for an hour.

SPEAKER_00 11:16

Well, of course, what it has to do with is your potential to get a disease. And and what that has to do with is who has been in the pool before you, and and how long has it been, and so on, because bacteria grow faster than algae does. One can become a million in about eight hours.

Algae Grows Fast When Ignored

SPEAKER_00 11:42

And the average person brings in about a hundred million bacteria with them when they come in. One of the things, one of the goals, the thing that we are trying to prevent in maintaining self-safe water is what we call bather-to-bather disease transmission. And what that means is you get in the water and you leave off your 100 million bacteria, and then I get in the water. And what protects me from your bacteria, and vice versa, because I get in the water and my 100 million get on get off of me and head for you. So, what protects both of us from making each other sick? And that that's called bather-to-bather disease transmission. And the only thing that stands between us to prevent that is the chlorine residual. That's it. Or sanitizer residual if you're not using chlorine. But something has to protect us from infecting each other. The residual of chlorine is the only thing that does that. And so if there's no residual, then all the bacteria that's been in that water and for however long it's had a chance to grow, is open season on you. You know, and and you can be affected by by a lot of it. And surely, you know, the the hundred million bacteria that's on you, probably a very small percentage of it is something that would make me sick, because we all have bacteria on us, and and all bacteria is not necessarily bad. So it's only the ones that are disease-causing that are a problem. So you may not have any disease-causing bacteria on you, but but then as most people do, they get water in their mouth, they don't want to swallow it, so they spit it back out, or their nose runs, or whatever, and they may pee a little or you know have a little pass a little gas or something in the water. And so there you have it. Now you got even you have bacteria that can cause a disease, and they multiply pretty quickly. The residual is the protection. That shield needs to be there. If you go swimming someplace that you're not sure of, the best thing you can do when you get out is to immediately

Zero Chlorine And Disease Risk

SPEAKER_00 14:13

or as soon as you can take a warm shower. Doesn't have to be a hot shower, but a warm shower. And the reason is that usually your pores are open when you're swimming. And you're exercising, the water's warm, so your pores are kind of opened up. And when you get out of the pool, your pores kind of close up because it's windy and you get kind of chilled when you get out. What you do is you go take a warm shower, and if you can use some soap, that's great, but at least use some warm water that will open up the pores that you have and it will flush out whatever's on there so it doesn't get trapped in your pores. And so, you know, once it's in your pores, it can make it into your body and your bloodstream and so on. If we can rinse that off as soon as you get out, then your chance of having a disease from getting in there is shortened.

SPEAKER_01 15:08

Yeah, it's good advice for for anyone that's that has that, or if they ever get in a pool with no chlorine to rinse in warm water to kind of help them from getting sick, if they had the potential of being sick from swimming in there. If you're looking for other podcasts, you can go to my website, swimming for learning.com. On the banner, there's a podcast icon. Click on that, it'll be over 1900 podcasts. We can download this at your leisure. And if you have the coaching program that offer you can learn more at poolcoaching.com. Thanks for listening to this podcast. Have a rest of your week. God bless.