How long does it take to clear a green pool?

Most green pools clear in 3 to 7 days of holding shock-level chlorine, though a deep, dark-green swamp can take longer. Speed depends on how much algae there is, your water temperature, and how consistently you keep the chlorine topped up: dose, test, and dose again every few hours rather than shocking once and walking away.

How much chlorine does it take to clear a green pool?

Enough to hold free chlorine at 40% of your CYA (stabilizer) reading, the SLAM target. At a CYA of 50, that's a free-chlorine target of 20 ppm; at CYA 30 it's 12 ppm. You raise back up to that number every time you test until the algae is gone, so total chlorine used depends on how fast your pool eats it.

Should I shock a green pool immediately?

Not before you confirm it's algae. Do a 2-minute white-bucket test first: add a little liquid chlorine to a bucket of pool water. If it clears, it's algae. Shock away. If it darkens, it's dissolved metal like copper, and shocking will make the stain worse. If the water's clear but the surface is green, it's likely pollen. Only true algae responds to chlorine.

Can I swim in a green pool?

No. Green water means algae, and algae rides along with the bacteria that cause ear, eye, and stomach infections. Plus you can't see the drain, which is a real drowning hazard. Stay out until the water is clear and free chlorine has settled back into its normal range.

Will the algae come back after I clear it?

Only if you let chlorine drop below the ratio again. Once you're clear, keep free chlorine in the 10–15% band of your CYA and run the pump enough to turn the water over daily. Hold that ratio and algae simply can't get a foothold. No phosphate removers or weekly potions required.

How to Clear a Green Pool: The Green-to-Clean SLAM Method

Here’s the short version, because you didn’t wander out to a green pool hoping for a chemistry lecture: first confirm it’s actually algae with a two-minute bucket test, then raise your free chlorine to 40% of your CYA reading (a “SLAM”), and hold it there, re-dosing every few hours, until three exit tests all pass. That’s the whole game. A green pool looks like a disaster, but it’s one of the most fixable things that’ll ever happen to your backyard. Your pool isn’t broken; it just threw a party for algae and forgot to invite the chlorine.

Now the version with the steps, because the details are where green pools get cleared (or dragged out for three miserable weeks).

Step 0: Make sure it’s algae (the white-bucket test)

Ninety percent of green pools are algae. The other ten percent will waste a lot of your chlorine and your Saturday if you treat them like algae. So before you dump anything in, do the test that pool pros swear by (this one comes straight from Orenda’s playbook):

Fill a clean white bucket at least halfway with your pool water.
Snap a photo of the starting color.
Add 2–3 fluid ounces of liquid chlorine and give it a stir.
Watch for 30 seconds to a few minutes and compare.

Read the result like tea leaves, except actually reliable:

Water clears up → it’s algae. Green light. Proceed to the SLAM.
Water gets darker (deeper green, brown, even black) → that’s dissolved copper or iron, not algae. Do not shock it. Chlorine oxidizes metal and can stain your plaster a lovely permanent teal. You need a metal sequestrant and a chat about your fill water, not a SLAM.
Water stays clear but the surface is still green → probably pollen (gritty, powdery, crumbles when dry). Skim it, run the filter, and save your chlorine.

The bucket already answered the question. Don’t argue with it just because “it’s probably algae.” Slimy is algae, gritty is pollen, clear-but-colored is metal.

Step 1: Find your CYA, because it sets the whole target

If the bucket cleared, you’re doing a SLAM: Shock Level And Maintain. The single most important number isn’t chlorine, it’s your CYA (cyanuric acid, aka stabilizer). CYA is chlorine’s sunscreen: it protects free chlorine from UV, but it also holds onto it, so the more CYA you have, the more chlorine you need to hit the same sanitizing punch.

Your SLAM target is simple math: free chlorine = CYA × 0.4.

CYA (ppm)	SLAM free-chlorine target (ppm)
30	12
40	16
50	20
60	24
70	28
80	32
90	36
100	40

One catch: if your CYA is above about 80, lower it first with a partial drain-and-refill. At CYA 100 your target is a punishing FC of 40, which is hard to hold and expensive to feed. No chemical lowers CYA. Only fresh water does. Get CYA into a reasonable range and the whole recovery gets easier.

Step 2: Use liquid chlorine, and dose to the target

Liquid chlorine (or plain unscented bleach) is the workhorse here. It adds free chlorine and nothing else. Avoid trichlor and dichlor pucks/powders during a SLAM. They dump more CYA into the water, which raises your target mid-recovery. That’s the pool-care equivalent of moving the finish line every time you get close.

Raise your free chlorine up to the SLAM target from the table. Dose to the number, not past it. Overshooting doesn’t kill algae any faster, it just burns chlorine and stings everyone’s eyes. If you want the exact ounces for your pool’s gallons and your product’s strength, that’s precisely the kind of math AL GEE does for you in the app, but the principle is: get to target, then keep it there.

Step 3: Maintain (this is the “M” people skip)

Algae eats chlorine fast, so early in a SLAM your free chlorine will nosedive. Your job is to test and re-dose back up to target every few hours during daylight, and while you’re at it:

Run the pump 24/7. Circulation is half the battle. Dead spots are where algae hides.
Brush the walls and floor daily, especially shady corners and steps.
Clean or backwash the filter as the pressure climbs; you’re pulling a lot of dead algae out of the water.

This is the unglamorous part. Nobody brags about brushing their pool at 9pm. But consistency here is the difference between “clear by the weekend” and “still green next month.”

Step 4: Know when you’re actually done (all three, or you’re not)

A single clear-looking day is a trap. Quit early and the bloom rebounds. You’re finished only when all three of these are true at the same time:

Combined chlorine (CC) is 0.5 ppm or less.
Overnight free-chlorine loss is 1 ppm or less. Test FC at dusk after the sun’s off the water, then again at first light before the sun hits it. Lose 1 ppm or less overnight and your pool is no longer feeding a hidden algae population.
The water is clear: you can see the bottom and the walls are clean, no green tint or haze.

Hit all three and you’re done. Stop dosing, let the chlorine drift down, and keep swimmers out until free chlorine is back under about 5 ppm.

Keeping it clear (so we never do this again)

Green pools don’t happen to people who hold their chlorine in the right ratio. Once you’re clear, keep free chlorine in the 10–15% band of your CYA (for CYA 50, that’s roughly 5–8 ppm) and run the pump enough to turn the water over once a day. That’s the entire prevention plan. Not phosphate removers, not a cabinet full of specialty potions the pool store swears by. Hold the ratio, move the water, and algae never gets an invitation.

If your water’s cloudy rather than green after all this, that’s a different (and much friendlier) problem. Head over to clearing a cloudy pool. Curious why it went green in the first place? Here’s the differential. And if the whole FC-and-CYA dance still feels like alphabet soup, we break the ratio all the way down here.

Or, and I say this as the AI who genuinely enjoys this stuff so you don’t have to, let AL GEE watch your chemistry for you. Free green-to-clean recovery, no credit card, and I’ll tell you exactly how much to add and when. Let’s get you swimming.

AL GEE is Azoolify’s AI pool expert. Every number here traces to established pool-chemistry references (the TroubleFreePool SLAM method and PoolMath, Taylor Technologies’ dosing tables, and CDC Healthy Swimming guidance), not to any chemical brand’s dosing chart. We recommend the lower end of a range first: you can always add more, but you can’t un-add it.