The service season here runs hardest from June through August, and by the end of it you have a fair idea what the summer was about. Looking back at mine, most of the new clients I picked up came to me because of algae. Almost every one of them had already spent weeks trying to fix it themselves.
Two things kept coming up. The first is that people fighting algae on their own almost always reach for algaecide, and algaecide will not clear a pool that has already turned. The second is that nearly every pool I service with an in-floor cleaning system, the kind with pop-up heads set into the floor, has at least one area where the water barely moves.
Different pools, different problems. What they have in common is where I ended up looking in both cases, which is how the water moves around a pool rather than what is dissolved in it.
Algaecide Will Not Clear a Green Pool
By the time somebody calls me about a green pool, they have usually been at it for 2 or 3 weeks, and the story is close to identical every time. They bought algaecide. They put it in. The water may have improved for a few days. Then the green came back, so they bought more algaecide.
One neighbor described it to me almost exactly that way. He kept adding chemicals, the pool would go normal, and 3 to 5 days later it was light green again. He had washed his filters twice that month. He was not being lazy about his pool. He was working hard on the wrong thing.
Algaecide is not an algae treatment. That is the part the label does not make clear. It is a preventive and a support product. It slows growth and it helps keep a balanced pool from tipping over. What it does not do is clear a pool that has already gone. Once you have a bloom, the algae has a food source, a surface to hold onto, and no working sanitizer opposing it. Algaecide does not fix any of those three.
There is also a specific way this goes wrong and costs you twice. A lot of what sits on the shelf is copper based. Copper is effective, and in hard water or at a heavy dose it can stain the pool surface. Las Vegas Valley fill water is hard before anything else happens to it, so the odds here are not in your favor. Buying bottle after bottle and ending up with a stained pool that is still green is the worst version of both outcomes. If you are going to run an algaecide preventively, polyquat is the better type, and the pool chemistry guide covers why.
None of which means algaecide has no place. Earlier this year I filmed a full recovery on a Las Vegas Valley pool, 4 days from a heavy bloom back to clear water. I said on camera during filming that the pool might end up needing an algaecide, and when I went back a month later it turned out it had. That is the right use for it: something you reach for once the pool is already clear, to stop it sliding back. It is not what clears the pool.
What Clearing a Bloom Actually Takes
Here is what clearing a bloom looks like, because this is the part people underestimate.
- Brush twice a day, 3 days in a row. Every surface, not a quick pass with the pole: walls, steps, the corners, anywhere growth can get a grip.
- A heavy shock load. On an average residential pool that lands somewhere close to 6 to 8 pounds, scaled up or down with the volume.
- A couple of other chemicals, depending on what the water is doing. The brushing and the shock are the backbone of it.
Six brushings in 3 days is the number that surprises people. This is not a problem you solve by buying the right bottle. It is physical work, repeated, while the chemistry holds. Algae anchors itself to the surface and shelters there. Brushing is what breaks it loose and puts it into water where the chlorine can actually reach it and the filter can take it out.
Algae Starts Where the Water Stops Moving
Why a bloom starts in the first place is a longer story, and I went through it in Why Pool Algae Keeps Coming Back in Las Vegas. That post names three causes: phosphates feeding the algae, a stabilizer level out of range, and a filter still holding the last bloom. After this summer I would add a fourth, and I would put it level with the other three.
1. Phosphates
The food source. Tap water, swimmers, and plant debris all bring them in.
2. Stabilizer
Too low and the sun burns your chlorine off. Too high and the chlorine stops working.
3. The Filter
A filter still holding the last bloom will seed the next one straight back into the pool.
4. Circulation
The one this summer moved up my list. A dead corner runs its own chemistry, whatever your test kit says.
Poor circulation is every bit as much a factor in an algae bloom as phosphates are, or a stabilizer level that has climbed too high, or not enough disinfectant in the water. I did not always weigh circulation that heavily. Working through a season of these changed my mind.
Algae thrives where pool water barely moves. Give two pools the same chemical treatment, and the one with poor circulation and dead spots is more likely to develop algae first, because the water never carries the sanitizer evenly through it.
Chemistry only works where the water goes. You can have perfect numbers on your test kit, from a sample you pulled at the steps, and have a corner of that same pool where the water has barely moved all week. That corner is running its own chemistry. It holds less chlorine than your reading says it does, and it has been sitting warm and still, which is exactly the condition algae is looking for. Blooms do not usually start everywhere at once.
So when I am working on a pool that keeps going green, I am not only reading test results. I am looking at where the return jets are pointed, how long the pump actually runs, and whether the filter is clean enough for either of those to matter.
Nearly Every Pop-Up Pool I See Has a Dead Spot
The second thing is a different problem on different pools, and it is the one I hold the strongest opinion about.
Before I get into it: this is my opinion, formed on the pools I service in the Las Vegas Valley. Plenty of people in this business will tell you the opposite, and they have arguments worth hearing. Here is mine.
I am not a fan of pop-up systems. There are positives, and the main one is that your pool stays clear of equipment: nothing floating in the water, nothing to haul out and drain, and the system runs on its own. On a pool where the layout makes a roaming cleaner awkward, that counts for something. If yours works and the floor really is clean, I am not telling you to tear it out.
The place I have seen them work well is on infinity edge pools. The pop-ups push debris toward the main drain, and they lift the lighter material to the point where it floats. From there the spillway takes over and carries most of it off. The cleaning system and the pool are working on the same job, which is not how it usually goes.
On the rest of them, what I find is different. Nearly every pop-up pool I have worked on has at least one dead spot. Somewhere on that floor is an area the heads do not reach, or do not reach with enough force to matter, and that is where everything ends up.
I also repaired three of these systems this summer. Heads that stopped rotating, heads that stopped coming up at all. I do not service hundreds of pools, so take the sample for what it is worth. Three in one summer still got my attention.
One of them is worth describing, because of what it showed.
Light bottomed pool, the kind where you see everything on the floor. I pull up and the water looks clean. Genuinely clean, the way you would want it to look when your service is working.
Then I shut the pump off.
Inside a few minutes, dust starts landing on the floor. A layer, across the bottom of a pool that looked spotless 5 minutes earlier. All of it had been in the water the entire time, held up in suspension, going around and around.
My read on it, and this is a read rather than something I can put a gauge on, is that the system was doing a good job of keeping dust moving and a poor job of getting it to the filter. If nothing had been stirring it, that dust would have been sitting on the floor where you could see it and where something could pick it up. Instead it was circling.
A roaming vacuum would have been down there lifting the dust off the floor instead of pushing it back into the water. Watching that pool is what decided it for me. In my experience a good roaming cleaner does the better job, and on most of the pools I see I would take one over an in-floor system. Somebody with a well designed system that is fully working may reasonably disagree with me. I would still tell them to run the check below.
Turn Your Pump Off for 20 Minutes
Here is something you can do this weekend, and it costs nothing.
- Let the pump run as it normally would, then shut it off.
- Walk away for 20 minutes.
- Come back and look at the floor of the pool.
- Anything you can now see on the bottom was being carried around in the water rather than taken out of it.
A clean pool stays clean with the pump off. What the test tells you is whether your equipment is taking material out of the water or only keeping it moving, which is exactly what a clean-looking surface hides.
Finding a dead spot is a separate check, and it takes a week rather than 20 minutes. Watch where debris gathers while the pump is running as it normally does. If the same corner collects every time you look, the water is not reaching it, and that corner is the part of your pool your chemistry gets to last.
Both checks work on any pool, with or without an in-floor system.
Fix a Dead Spot Now, Not in July
Nobody in the Las Vegas Valley is calling late September cool. The days are still running in the 90s. What has changed is the nights, and the nights are what your water responds to.
Through July and August the pool never really got a break. It gave back a little heat overnight and had it all back by mid-morning. Now it holds cooler through the night, and that carries into the day. Algae slows down. Chlorine stops burning off as fast as you can put it in. The margin you have been running without since June starts to come back.
That is what makes this the right stretch to look at circulation. In July, chasing down a dead spot means fixing equipment and fighting the water at the same time, and the water is winning. Right now you can work the problem on its own.
If you shut your pump off this weekend and found something sitting on the floor, deal with it while the weather is on your side.