A pool turns green when the free chlorine drops too low to keep algae in check, and algae grows fast enough to cloud the water within a day or two. In Queen Creek's summer heat, that can happen after a single missed week, a pump that stopped running, or one dusty monsoon storm.
The good news is that almost every green pool can be brought back without draining it. How long it takes depends on what kind of algae you have and how far it has spread.
Why pools turn green so quickly here
Algae spores are always blowing into your pool. Chlorine kills them as they arrive. When chlorine runs out, nothing stops them, and warm, sunny water is exactly what algae likes.
Several things in the East Valley use up chlorine faster than in milder places:
- Heat and sun. Sunlight breaks chlorine down, and warm water speeds up algae growth. A pool that holds chlorine fine in March can run dry in a few days in July.
- Monsoon dust and debris. Storms from July through September carry dust, leaves and organic matter into the water. All of it uses up chlorine.
- A stopped pump. If the pump or timer quits, water stops moving through the filter and the chlorinator. Still, warm water can turn in a day or two.
- Too much stabilizer. Cyanuric acid (CYA) protects chlorine from the sun, but chlorine tablets keep adding it. When CYA builds up too high, chlorine still reads on a test strip but works much more slowly. This is one of the most common reasons a pool keeps going green even though someone is adding chlorine.
- Low circulation hours. Running the pump only a few hours a day in summer leaves water sitting too long between filter passes.
The three kinds of algae
Not all green is the same. What you're seeing affects how the pool gets cleared.
Green algae. The most common type. It floats in the water and clings to walls, turning the pool anywhere from slightly hazy to opaque green. It responds well to a proper shock and brushing.
Mustard (yellow) algae. It looks like yellow or brownish dust, usually on the shady side of the pool, and brushes off easily but comes right back. It tolerates normal chlorine levels, so it needs a higher dose held for longer, and pool tools, floats and swimsuits have to be cleaned too or they reintroduce it.
Black algae. Dark spots with raised edges that don't brush off. Black algae roots into plaster and pebble surfaces and has a protective outer layer, so it needs hard scrubbing with a stainless brush plus a focused chlorine treatment. It's the slowest to get rid of.
Why shock alone often doesn't work
Pouring in a few bags of shock is the first thing most people try, and it often fails. The usual reasons:
- Not enough chlorine. Clearing algae means raising chlorine to a level based on your stabilizer level and holding it there until the algae is dead, not just adding a fixed amount once.
- High stabilizer. If CYA is very high, it can take an impractical amount of chlorine to clear the pool. Partially draining and refilling to dilute it is sometimes the cheapest fix.
- No brushing. Algae protects itself on the walls and floor. Brushing breaks it loose so the chlorine can reach it.
- A dirty filter. Dead algae ends up in the filter. If the filter isn't cleaned during a cleanup, the water stays cloudy for days.
How long a green pool takes to clear
Most green pools clear in three to five days, over several visits:
- Day one. Test the water, adjust pH, shock to the right level, brush every surface, and run the pump around the clock.
- Days two and three. Keep chlorine high, brush again, and clean the filter as it fills with dead algae. The water usually turns from green to cloudy blue-gray.
- Days three to five. Vacuum dead algae off the floor, clean the filter again, and balance the water once it's clear.
A pool that has turned black, or is full of leaves and debris after sitting empty, can take a week or more. Sometimes draining is faster and cheaper than trying to clear it.
DIY or call a pro?
If the water is only slightly hazy and you caught it within a day or two, a homeowner with a good test kit can usually clear it. Test for free chlorine and stabilizer, raise chlorine accordingly, brush, and run the pump.
It's usually worth calling a pro when:
- You can't see the bottom of the deep end
- You've already added shock and it's still green after 48 hours
- You see mustard or black algae
- The pump or filter isn't working properly
At that point, the cost of chemicals from repeated attempts adds up quickly. Light to moderate green pools commonly cost $350 to $800 for a professional cleanup, and very dark pools more. A pro will also find out why it happened, so it doesn't happen again next month.
Keeping it from coming back
Once the water is clear, steady chlorine is what keeps it that way. Weekly service, enough pump hours in summer, a clean filter, and stabilizer kept in a sensible range prevent nearly every green pool.
If your pool in Queen Creek, San Tan Valley, Gilbert or Florence is still green after 48 hours, a local pro can usually clear it in a few days. Send a request below or call (480) 788-5344.