Cal-Hypo and Black Pool Stains: Bob Lowry Explains

A black stain appears the moment cal hypo hits the floor—panic sets in. We unpack why that stain isn’t a new disaster but copper changing form, and how to turn a scary moment into a clean, controlled fix. With guidance from Bob Lowry, we break down the chemistry that matters, the tools that actually remove metals, and the habits that keep stains from returning.

We start with the copper story: how copper sulfate hides in plain sight until oxidation turns it into black copper oxide, and why ascorbic acid can lift the look without solving the load. Then we get practical. We compare sequestrants and chelants, explain why they degrade under chlorine, UV, ozone, and AOP, and outline two reliable removal paths: CuLator capture over days or a pre-filter loop that strips metals in hours. We also cover partial drain and refill strategies and the simplest operational safeguard—dissolving and distributing cal hypo instead of letting granules settle on the floor.

From there, we shift to living threats. Algae divisions add up fast, and by the time you can see it, a biofilm likely shields it from chlorine. We share a straightforward plan: brush to break the polysaccharide layer, raise sanitizer deliberately, and avoid the costly mistake of “waiting a week.” Finally, we tackle the health side that too many ignore: zero chlorine means no barrier against bather-to-bather disease transmission. People bring millions of bacteria into the water; residual sanitizer is the only real-time shield. If you do end up in water with no sanitizer, take a warm shower right away to reopen pores and rinse contaminants before they cause trouble.

• honoring Bob Lowry’s contributions to pool chemistry
• why cal hypo can turn hidden copper blue-green to black copper oxide
• pros and cons of ascorbic acid on stains
• how sequestrants work and why they degrade
• practical metal removal with CuLator and pre-filters
• safer cal hypo application and dosing tips
• algae growth math and biofilm protection
• brushing strategy to break polysaccharides
• risks of zero c

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Chapters

• 0:00 Honoring Bob Lowry’s Legacy
• 3:12 Sponsor Message And Coaching Invite
• 3:13 Why Cal Hypo Triggers Black Stains
• 6:23 Removing Metals: Tools And Tradeoffs
• 8:44 Ignoring Early Algae Growth
• 8:53 Cal Hypo Handling And Application Tips
• 13:20 Brushing, Biofilms, And Best Practice
• 16:42 Swimming With Zero Chlorine Risk

Transcript

SPEAKER_00: 1:02

Hi, welcome to the Pooh Guy Podcast Show. Talking to Terry Arco earlier in the week, I decided to bring back a few episodes with Bob Lowry. I think it's important, since we're talking about his legacy, to kind of share some of the episodes that I recorded with him. I have a lot of podcast material with Bob Lowry, which is fortunate for the industry. And in today's podcast, he's going to talk about a black stain forming when you pour cal hypo in a pool, which does happen in situations, and I've had this happen. Other people that I know have had this happen as well. And I also asked Bob Lowry what happens if you swim in a pool that has no chlorine in it, which is something that can happen out there, and I think he gives a really good answer to that. So enjoy I hope you enjoy these uh next three days of podcasts with Bob Lowry again. And Bob Lowry, of course, had just a great knowledge of chemistry, as well as insight in other areas of the pool service industry and pool service business. 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 swimmingpoollearning.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_01: 2:43

Well, the first thing is it probably scares you to death. Because you're, you know, what goes through your mind is, oh my God, I'm gonna 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 the the stain is copper, and it's copper sulfate, and it's kind of a blue color, the water's blue, and especially at 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's 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 pre-filters 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 to drain some water and refill it.

SPEAKER_00: 7:22

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_01: 7:28

Well, you 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.

SPEAKER_00: 7:55

Here's one. And this happens a lot with a lot of new pool techs. What if you see algae in the pool? It may be 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 cut you're kind of ignoring the algae problem the first week you see it?

SPEAKER_01: 8:19

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 algacy 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 grow.

SPEAKER_00: 10:55

And that reminds me my son, my son likes to tell his friends this one. 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_01: 11:30

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_00: 11:42

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_01: 12:01

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. 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 off 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 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_00: 15:53

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 interested in other podcasts, if you go to my website, swimming for learning.com, click on the podcast icon on top. It'll take you to a drop down menu of eighteen hundred podcasts there. If you're interested in the coaching program that I offer, you can learn more at foolguycoaching.com. Thanks for listening to this podcast. Have the rest of your week, and God bless.