Black Algae: Can You Accidentally Infect Another Pool?

Black algae can turn a clean pool into a never-ending battle, and the worst part is you might be spreading it yourself without realizing it. We dig into what “black algae” really is (often cyanobacteria), why it clings so stubbornly to plaster, and why the usual quick shock routine often fails unless you do the one step most people skip: aggressive brushing to break the protective heads so chemicals can reach what’s underneath.

We also get specific about transmission and cross contamination. Spores can hitch a ride on anything wet, from a bathing suit that went from the ocean to the pool, to the damp tools riding in the back of a service truck. We talk through the biggest culprits, including nets, leaf rakes, bags, and especially stainless steel brushes, plus how low free chlorine levels make the next pool far more likely to “catch” black algae after exposure.

Then we lay out a practical pool maintenance plan for black algae treatment and prevention: how to approach superchlorination safely, when topical products like granular trichlor or broken cal-hypo tablets can help, and how copper options (including chelated systems like PoolRx) fit into longer-term control without creating staining issues. If you want fewer callbacks, fewer route-wide outbreaks, and a clear plan for stopping black algae from coming back when chlorine dips, this one is for you. Subscribe for more pool service training, share this with a tech who needs it, and leave a review with your toughest black algae question.

We break down why black algae is so hard to kill, why it often comes back, and why it is more like cyanobacteria than typical pool algae. We also explain how black algae can spread from pool to pool through damp tools and low chlorine, plus the practical steps we use to treat it and prevent cross contamination.
• What black algae is and why it resists normal shocking
• How spores can hitchhike on wet suits, towels, and pool tools
• Why brushing the heads off is nonnegotiable for treatment
• When superchlorination works and why circulation matters
• Granular trichlor and cal-hypo tablet options for topical killing
• Copper approaches like PoolRx and dosing cautions to avoid staining
• Dedicated nets, rakes, and stainless brushes to stop route-wide spread
• The “never let chlorine hit zero” rule after a black algae cleanup
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. If you're interested in the coaching program that I offer, you can learn more at poolguidecoaching.com.

Support the Pool Guy Podcast Show Sponsors! 

HASA 
https://bit.ly/HASA

The Bottom Feeder. Save $100 with Code: DVB100
https://store.thebottomfeeder.com/

Try Skimmer FREE for 30 days:
https://getskimmer.com/poolguy 

Get UPA Liability Insurance $64 a month! https://forms.gle/F9YoTWNQ8WnvT4QBA

Pool Guy Coaching: https://bit.ly/40wFE6y

Transcript

Welcome And The Big Question

SPEAKER_00 1:02

Hey, welcome to the Pool Gay Podcast Show. It is in a minute to talk to you about black algae. I'm going to answer some of the questions concerning spreading black algae from pool to pool. Is this possible and should you be worried about using your pool equipment in one pool that has black algae and possibly spreading it to another pool? 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. And I remember distinctly when I first saw my first black algae. This was when I was working back, I believe it was in 1989, 1990, right around there. I was working in a pool in Ontario, California, and this pool had a sand filter, which wasn't typically wasn't typical of the area. I remember that distinctly. But I also remember that this is where I first saw the black algae on the plaster in the pool. The sand filter just kind of triggered my

Coaching Program Quick Pitch

SPEAKER_00 2:11

memory because they're pretty rare here. And I remember the black algae, and I remember treating it, brushing it, and nothing happening to it. There was really not a lot of literature on what to do with it. And the person I was working for back then said, Oh, just put some you know chlorine on top of it, and

First Black Algae Encounter

SPEAKER_00 2:30

that should kill it. I've you've seen it before, whatever. So I did put some chlorine on top. We we used to get the tablets in these giant drums, and there was a lot of the trichlorid dust still on the bottom. So I took some of this and I sprinkled it, spread it on the pool, and and luckily it was a white plaster pool, by the way, because there was no cautions or kind of explanations or any kind of training. He just said put some some of this powder on it, it'll kill it. And it did take care of it. And that was the first instance of black algae. And I think there hasn't been a lot of knowledge since Rudy Stinkowitch wrote his book on algae, where he really talks about black algae in detail, and that actually black algae is not even an algae, it's it's actually a cyanobacteria. And it looks like algae, of course, because it forms on the surface, and you know, we kind of think that it's just like green algae or yellow algae, but it's actually more aggressive, and the roots go really deep into the pool. That's why you hear these stories of like someone who had black algae, they replasted their pool, and the black algae was still there. Now, I don't know how far you can believe that. It could be true, but it could just be that the spores were still in the area. Now, how does the black algae get into the pool? Well, it's interesting because the theory

What Black Algae Really Is

SPEAKER_00 3:47

about it getting in from like the beach on the bathing suit is not too far from the truth if if you analyze you know where the black algae comes from. So, yes, oceans, you know, wherever the cytobacteria spores exist in nature, they can attach anything wet, believe it or not, like a wet bathing suit or a wet t-shirt or a pool brush or a leaf rake that stays wet for a little bit of time, it survives on there for quite a long time. I think up to weeks it can survive on there, the spores of the black algae. So it's not really a stretch or a urban legend that black algae maybe originated from the ocean and got on someone's bathing suit that used it in the ocean and the pool, because truthfully, you're not gonna use different bathing suits in the ocean or lake in a pool. And I could have gotten into the first pool that way. You know, I was recently in Iceland on a vacation and they don't have mosquitoes there, but one of the one of the persons living there had told me that they actually had their first like sign of mosquitoes recently in one city. And so maybe mosquitoes are invading Iceland in the future. But it would be nice to have a place where there were no mosquitoes, I guess. But it's one of those things where eventually it's going something's gonna happen and something's going to invade the area. So black algae, I think I was pretty close to when it was hitting California back in the early 90s, is when we first started seeing the black algae. Prior to that, I don't think it was extremely prevalent, and I think a lot of that has to do with maybe knowledge and kind of recognizing what it is. Maybe no one reported it as much. But I would say that yes, like a towel or anything you're using at the beach and using your pool. Let's say you have a brand new pool built and you want to prevent black algae from ever growing in that pool. I would highly recommend that if you go to the ocean, that the kids don't use the same bathing suits for the pool, kind of keep everything separate. And if you do see black algae at all in your service account, you want to attack it pretty aggressively. So I mentioned the trichlor powder that was at the bottom of the tablet buckets that we would use. Hasa makes something called algae ban, which is a granular trichlor. I find it highly effective against black algae, not only because it raises the chlor level to like 100 parts per million, but the black algae is really hard to kill. There's like a coating on top. If you ever treated

How Spores Get Into Pools

SPEAKER_00 6:17

a pool with black algae, you know what I'm talking about. You would take like a five-inch or six-inch stainless steel brush and try to brush the heads off, and it would be kind of like a light brown color once you brush the head off, and then the chlorine will actually have much more effect than killing it. You just can't superchlorinate the pool without brushing it. In most cases, that's not going to have the same kind of effect or the killing factor or the killing power on the black algae

Proven Treatment Methods That Work

SPEAKER_00 6:43

itself. So I would definitely recommend brushing the heads off and the superchlorinating. If you're uncomfortable using the granular trichlor, then you would just superchlorinate the pool. You can also use a copper algae. The Pool Rex Plus is very effective against black algae as well. It does take some time for it to actually kill it. Copper is known to kill the bacteria or the blackout or the cyanobacteria, so copper is good and it is effective against it. But I think the most effective treatment does require superchlorination, the use of copper, and maybe some granular trichlor used correctly if it's if you sprinkle it on lightly. You can also use, you know, I found what would be an effective alternative to this, and if you have calhypotablets, you can actually break these up into chunks, maybe not as small as the granular trichlor, and these will also sit on top the black algae and kill it as well. Anything that's topical that can sit on top of it, and calhypo, by the way, won't burn the pool plaster like the trichlor trichlor granular may if you don't put it on correctly. So grinding up some calhypotablets or breaking with a rubber mallet in a plastic bag may be as effective as the granular trichlor that you're using out there. I found that using the trichlor the um calipotablets, I should say, is a great alternative because they dissolve slowly in the water and they'll sit on top of the black algae heads as well. Since I mentioned that the first outbreak of black algae probably came from someone swimming in the ocean that had the black algae on their bathing suit, then how was it transferred to you know several pools across the area, and then of course is found in a lot of pools now across the area. Well, I think a lot of it is cross-contamination with your pool pool cleaning tools. I mentioned that if the surface is damp and a pool brush or pool leaf rake coming from one account to another is going to be pretty damp still with the water on it from the pool, there's a possibility that the black algae spores are on the pool brush or on the pool net and it could be transferred from one pool to another pretty easily. Now there's a few factors involved in transferring the black algae. I think a lot of it has to do with the chlorine level in the pool itself. If the free chlorine level is low, like one part per million or less, and you're going from one pool to another, you're going from one pool of black algae into a pool that has a really low chlorine level, the chances of you transferring the black algae are greater than if that pool had you know five parts per million of chlorine in it, and it was fine

Cross Contamination From Cleaning Tools

SPEAKER_00 9:57

as far as the sanitizer level. So low chlorine is a contributing factor to the spread of black algae. If you ever shooted a pool with black algae and then the chlorine zeroed out the following week, there's a good chance that the black algae has come back with a vengeance because again, chlorine is somewhat effective in killing or keeping the black algae from spreading and increasing. And if you're transferring your skimmer leaf rake and brush into a pool that has very low chlorine, there's a good chance that the black algae from one pool can enter another, and you could have several black algae pools on your route after that. So I recommend that if you have a pool of black algae, use a dedicated leaf rake and a dedicated brush. I wouldn't worry too much about the pole. The pole is gonna dry out between stops pretty rapidly, and I think the spores are probably looking for more of a cloth-like material, like a ripttide bag would be very risky. If you're using the riptite in a pool with black algae and take it to another pool and use it, chances are the bag is gonna have spores in it, release them into the water, and if that chlorine level is low in that pool, black algae can spread very rapidly. Will it stay in your pool vacuum hand? Again, it may dry out before you get to the next stop. There could be some black algae on the wheels. The pool hose, possibly there might be some spores on there. I find that leaf rakes, of course, and nets are the leaf rakes, nets, and brushes are probably the biggest contributor to black algae in one pool to another. So you definitely again want to take precautions with your equipment and you don't want to spread the black algae from pool to pool or try to prevent it as much as possible from spreading. So, of course, if you're using a six-inch stainless steel brush in the pool to break the heads off the black algae, I can almost guarantee you that brush is extremely contaminated with black algae. It's gonna have some of the residue of the heads on there, and there's no question that you're going to spread the black algae from pool to pool using your stainless steel brush. So, of course, have a dedicated six-inch stainless steel brush. It makes no sense to not use the same leaf rake and brush, but then you're using a stainless steel brush in the pool. That definitely needs to be something that you leave at that site and use that stainless steel brush only on that pool because that will spread the black algae pretty fast. Now, if you if you are treating it again, you have to brush the heads. That's kind of mandatory to treating black algae. If you don't brush the heads off, the chemical will penetrate. I don't think the copper will penetrate as easily as well with the heads on the black algae. So you want to brush them off. Sometimes it's a real pain, and it is black algae all over the place. And so this may take like half an hour sometimes. I've believe me, I've done this where I spent half an hour brushing black algae in 90-degree weather on a pool surface, so there is a lot of manual labor. Of course, you're gonna charge for the black algae treatment because you can't do this at no charge. You're you're brushing the pool, treating it, raising the chlorine level, and spending extra time there. So you want to make sure that the free chlorine level is at least 30 parts per million or higher. I found that if it's any less than that, if the black algae is not killed or destroyed properly.

Brushing And High Chlorine Protocol

SPEAKER_00 13:14

So I always raise the pools at 50 parts per million and keep it at that level for a few days so that the chlorine really has a chance to kill it. You'll be amazed if you use the granular trichlore, the algae band, and you have a pool that has like a really big outbreak of black algae. If you were to spr sprinkle that and broadcast it on the pool surface, and you go back there the next week and the black algae is pretty much gone. Of course, the automatic cleaner should be turned off for that period of time so that it doesn't pick up the chlorine. So turn off the automatic cleaner. And I wouldn't say the pool needs to necessarily be off, but when you're broadcasting the algebrain in the pool, the pool should be off so that it settles without being blown around. But then the pool could probably run a few hours after that. If you're super chlorinating the pool, not using the granular trichlor, you definitely want to run the pool 24-7 to kind of get the most circulation to ensure that the spores are entered enter into the filter. You clean the filter out and get rid of that. And of course, one of the things that you want to make sure is that you no one goes in the pool while the pool's at 50 parts a million. That's one thing. And you want to make sure that no one's in there and that the pool doesn't get turned off during the process. Sometimes homeowner will be like, hey, the pool's running at 11 o'clock at night, let me turn it off. That could short circuit it, and you want to make sure it's circulating as long as possible with the high chlorine level, and you want to keep it at 50 parts per million the best you can during the whole week period, you know, a few days during the week at least it can drop down to like 30 after that. But you definitely want to superchlorinate it, and then after the fact, the chlorine can really never zero out after the pool has had black algae. I've seen this happen where the pool is perfectly cleared of it, and you know, even a year goes by, but then they have a pool party and the pool goes to zero. And sure enough, the little pinhole black algae starts to develop again in the pool. You know, there's there's these trees that are out here in the area that will just kind of sprout out and grow everywhere, and you'll cut it down, you'll even cut it down to where there's a stump, and then the tree will start growing right back out of the stump if it gets a little bit of moisture in there, even if you poison it. It's a really aggressive tree, and it's really like a plague in my area. It's all over the place, and kind of black algae is very similar that if the chlorine does zero out for any period of time, the heads could develop redevelop because they're they're probably the roots are probably still under the plaster, they go pretty deep. And if the chlorine

Keeping It From Coming Back

SPEAKER_00 15:46

level is always, you know, five parts a million, you know, all through the summer, you don't have much to worry about. But if it does zero out, then you have a little bit of a problem. And so one way to ensure that the black algae will be eliminated is to of course put copper in the water to a safe level. The safest way to introduce copper, in my opinion, is with the pool RX because it's chelated, it's not gonna fall out of solution and stain the pool. You can use a copper algacyte every week, but you gotta be careful that you don't overdose the pool with the copper, because if you put too much copper in there, it could cause staining in the pool. So definitely copper is a great thing to have in your pool going forward after black algae, and it also helps treat it again. It just takes a long time for it to actually kill it and destroy it, and you have to make sure that you brush the heads off the black algae. So I guess to summarize, if you are doing pool service and you notice the account has black algae, I would not reuse the same riptide bag, the same brush, the same net in the pool, because you can spread the black algae from one account to another if the conditions are correct in that pool to allow the black algae to form and grow. And to prevent that, just keep separate equipment at the pool of black algae. And even after you cure the black algae, I kind of would be reluctant to still use the same brush and net, you know, unless you know for sure like months have passed that there's no black algae in there. And it's again something that can come back at any time if the chlorine level drops down. So better not to have black algae because treating it and preventing it in the future is a real pain. And the best thing to do is not to cross-contaminate your pools with your pool equipment. Looking for other podcasts, you can find those on my website,

Final Prevention Rules And Links

SPEAKER_00 17:30

swimmingpoollearning.com. Click on the podcast icon on the banner. There'll be a drop-down menu of over 1900 podcasts for you there. And if you're interested in the coaching program that I offer, you can learn more at poolguidecoaching.com. Thanks for listening to this podcast. Have the rest of your week and God bless.