You walked out back and the pool is green. Maybe light green, maybe full swamp. Either way, nobody's swimming in that. This is the most common service call we get in Dallas from May through September, and it's fixable. Most green pools go from unusable to swim-ready in 48 to 72 hours.
Here's what's happening and how to fix it.
Green water means algae. Algae needs two things: low chlorine and warm water. Dallas hands out both of those generously from late April through October.
The usual triggers: you went on vacation and nobody maintained the pool. The pump failed and you didn't notice for a few days. A big storm dumped debris and organic material that ate through your chlorine. Or you just fell behind on chemical adjustments during a heat wave.
In a 100-degree Dallas week, a pool can go from clear to green in four days. That's not a scare tactic. That's what happens when free chlorine drops below 1 ppm in water that's running 88 to 92 degrees. Algae thrives in exactly those conditions.
Not all green pools are the same. The fix depends on how far things have gone.
Light green, still translucent: you can see the bottom, but the water has a green tint. Chlorine has dropped but algae hasn't fully taken over. This is the easiest fix. A heavy shock, good brushing, and 24 hours of filtration usually clears it.
Dark green, opaque: can't see the bottom. The water looks like pond water. Algae is established on the walls and floor. This takes two to three days of treatment with multiple filter cleanings.
Black-green swamp: standing water with no circulation, possibly mosquito larvae, thick algae on every surface. This is a multi-day recovery that might require a partial drain, acid wash, and equipment inspection. If the pump hasn't run in weeks, the motor might need service before you can even start the chemical treatment.
Don't swim in a green pool. Algae itself isn't always dangerous, but the bacteria that thrive alongside it can cause ear infections, skin rashes, and gastrointestinal illness. Clear the water before anyone gets in.
Net out as much leaves, sticks, and floating material as you can. Don't vacuum yet. You'll just clog the filter. Get the big stuff out by hand or with a leaf rake. This step matters because every piece of organic debris in the water is consuming your shock treatment.
Brush the walls, floor, steps, and any crevices. Algae anchors to surfaces and forms a protective layer that chlorine can't penetrate. You need to physically break that layer up. Use a stainless steel brush on plaster pools and a nylon brush on vinyl or fiberglass. This is the step most people skip, and it's the reason their shock treatment doesn't work.
For a standard 15,000-gallon pool that's moderately green, you're looking at 3 to 5 pounds of calcium hypochlorite shock. Dark green or black pools might need 5 to 10 pounds. The target is to get free chlorine above 30 ppm and hold it there. Half measures don't work with algae. A light shock on a dark green pool just feeds the problem. Dose at dusk so the sun doesn't burn the chlorine off before it works.
Keep the pump running nonstop until the water clears. No timer, no off-hours. The filter needs to be cycling continuously. Check the filter pressure every 8 to 12 hours. When it climbs 8 to 10 psi above your clean baseline, backwash or clean the filter. You might need to do this two or three times during recovery.
Test free chlorine the next morning. If it's dropped back below 5 ppm, the algae consumed your first dose. Brush again, shock again. Repeat until chlorine holds above 5 ppm for at least 12 hours. That's when you know the algae is dead.
Once the water goes from green to cloudy gray or milky white, that's dead algae settling on the floor. Vacuum it to waste if your system allows it. If you vacuum to the filter, you'll need to clean the filter again immediately after. Run the pump for another 24 hours after vacuuming and the pool should clear.
The two most common mistakes we see: under-shocking and not brushing. People buy one bag of shock, dump it in, and expect miracles. On a dark green pool, one bag isn't close to enough. And without brushing, the shock can't reach the algae that's bonded to the plaster.
The other problem is filter capacity. Most residential pool filters aren't sized for the amount of dead algae a full recovery produces. If you're not cleaning the filter multiple times during the process, the water stays cloudy because the filter can't handle the load.
Dallas heat complicates things too. Chlorine degrades faster in 95-degree water than in 75-degree water. What works in a moderate climate might not be enough here. You burn through chemicals faster, which means more product, more testing, more adjustments.
Light green: 24 to 48 hours with proper treatment. Dark green: 48 to 72 hours with aggressive treatment and filter cleaning. Black-green swamp: 5 to 7 days, sometimes longer if equipment needs repair first.
Don't swim until the water is clear, free chlorine is between 1 and 5 ppm, and pH is between 7.2 and 7.6. You should be able to see the main drain clearly from the deck. If you can't, it's not ready.
In Dallas, green pool recovery runs $300 to $800 depending on severity. A light green caught early is on the low end. A full swamp that hasn't had circulation in a month is on the high end. Most companies charge a flat rate based on what they see when they arrive. Chemicals, multiple site visits, and filter cleaning are typically included in that flat rate.
If you've tried the DIY route and you're two shock treatments in with no improvement, call a pro. You'll spend more on chemicals doing it wrong than the service costs to do it right.
Fill out the form and we'll get back to you within 2 hours. Most recoveries start same-day or next-day.
Get help fast →