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Pool Keeps Turning Green? Here’s Why (+ How To Fix)

Swimming pools should be clean and clear, not green and cloudy. The discoloration is often a sign of a hazardous swimming environment, so it should be dealt with immediately. Your pool filtration system handles the cloudiness. If it’s not working properly or there’s too much to handle, it could damage the equipment.

If your pool keeps turning green, here are the likely reasons:

  • Algae growth
  • Copper in the water
  • Dirty pool filter
  • Debris on the tile line
  • Stained pool liner
  • Organic matter in the pool
  • Dirty light fixture

In this post, I’ll explain why each of these problems can cause your pool to turn green, what you can do about it, and how you can prevent them from happening.

Algae in the Water

Algae can quickly turn your pool green. In fact, algae is the most common explanation for a green pool. If your pool looks dingy and discolored, it’s time to find the source of the bloom and get rid of it. Too much algae in the water can make it dangerous to swim in the pool.

Here’s a list of reasons you have algae in the water:

  • Too many phosphates can cause algae blooms. Phosphates are algae’s primary food source. They’re brought into the pool by pets, fertilizer, people, and other organic materials.
  • Your pool doesn’t have enough chlorine. A lack of sanitizer will undeniably lead to algae growth. If there’s nothing to stop the algae, it’ll bloom in a few days.
  • The filter isn’t cycling the water often enough. Your pump should run for one hour per ten degrees Fahrenheit. If it doesn’t run enough, the sanitizers and other chemicals can’t dissolve and circulate in the pool.

How to Fix

Here’s how to quickly remove green algae’s discoloration from the pool:

  • Use a pool vacuum for algae. Pool vacuums quickly remove algae without leaving the pool cloudy.
  • Overdose your pool with two times the amount of chlorine that you usually use. Chlorine neutralizes algae, but it’s used up when it eliminates the bacteria.
  • Clean your pool filter and use a water clarifier to catch additional particles. Water clarifiers reduce your filter’s micron density to grab finer debris.

The Robarb Pool Clarifier comes in a 32-oz bottle that offers more than enough treatments for several years. Place the clarifier in the skimmer basket, turn on the pump, and watch as the water gets much clearer. This clarifier can be used to remove living or dead algae, making it the perfect combination.

Robarb Pool Clarifier

Too Much Copper in the Pool

Copper can turn your swimming pool green. It’s a crucial part of maintaining a healthy pool, but overloading the water can ruin the equipment. Most algaecides have copper in them since copper removes dead algae from the pool. You can test your pool with copper test strips to ensure there’s not too much of it before adding a copper-based algaecide.

Another reason your pool might have too much copper is if you have copper plumbing. Most swimming pools have PVC or corrugated plastic hoses. Old-school pools sometimes have copper plumbing that needs to be replaced as quickly as possible.

How to Fix

Unfortunately, the only way to remove copper from the water is through dilution. You’ll have to drain a foot or two of the water, then refill it to dilute the copper’s concentration. Make sure you never drain more than ⅓ of the water at a time. Drain, refill, and test for copper. Also, keep the pump off when the water is below the skimmer basket.

Dirty Filtration Systems

Your filter needs to be cleaned regularly. If you have a dirty filter, it won’t catch the algae and other debris in the water. Furthermore, it could leak some of the debris back into the pool. You can run the pump 24 hours a day without noticing a difference.

It’s important to remember that the pool’s filter is one component of the filtration system. You also have to clean and maintain the pump, skimmer basket, plumbing, unions, salt system, and heater. If any of these components aren’t cleaned, they’ll turn the water into all sorts of unwanted colors.

How to Fix

Clean your pool filter with these steps:

  1. Turn off the pool pump.
  2. Backwash the filter if you have a sand or DE filtration system.
  3. Open the filter and spray the cartridges or fins if you have a cartridge or DE filtration system.
  4. Add media if necessary (this only applies to DE and sand pools), or replace the cartridges if they’re torn.
  5. Seal the filter, turn on the pump, and make sure the filter gauge doesn’t exceed 25 PSI.

The best way to know if your filter is dirty is to keep an eye on the pressure meter. It should stay between 10 to 20 PSI. When it gets too high, the filter is clogged, or one of the baskets is full. If it’s too low, there might be air in the system, or the pump is running on low RPMs.

Debris on the Tile Line

A dirty tile line can turn the pool green, yellow, brown, or cloudy. Pools with tile lines absorb a lot of algae and other debris. This debris traps itself in the porous grout, causing long-term discoloration. It can be very difficult to manage a dirty tile line once the debris gets too far into the grout or plaster.

Another reason you might have a green-colored tile line is if you don’t have enough water in the pool. The water level should be well above the skimmer basket. If it’s too low, the water will leach calcium and algae into the tile because it dries from the sunlight.

How to Fix

Scrub the tile line with an abrasive sponge. You could also use pumice stones if you have rough tile grout in a plaster pool. Another option is to scrub the tile with a chlorine tablet, though you’ll need safety gloves and glasses.

The best way to prevent stained tiles is to brush the pool weekly. Some pool vacuums climb the walls, but brushing is irreplaceable.

Stained Vinyl Liners

Vinyl liners are prone to staining. Algae, copper, and other substances can stain the liner, turning it into various colors. If the liner is stained, the color will reflect into the water. You can have a crystal-clear pool, but the dirty liner will make it look like a lake. Your vinyl liner won’t last long if it’s stained because it could corrode.

Plaster and fiberglass pools can stain, but you can typically remove the discoloration with a brush. However, a deep stain in a vinyl liner can be permanent if it’s not treated soon enough.

How to Fix

I recommend brushing your vinyl liner with a soft bristle brush one to two times per week. Small algae blooms can go unnoticed, staining the vinyl and making it very difficult to clean. Light blue liners are very susceptible to staining. High-end vinyl liners are often treated for algae blooms, though.

The LALAPOOL Swimming Pool Brush is a soft 18-inch brush that attaches to any universal telescoping pole. It has curved edges to clean walls and slopes in the pool. Furthermore, it has ultra-soft bristles that won’t damage the vinyl, plaster, or fiberglass.

LALAPOOL Swimming Pool Brush

Organic Matter in the Water

Unless your pool is airtightly sealed from edge to edge, organic matter will inevitably land in it. Trees, bushes, dirt, grass, hair, fur, and other substances will discolor your swimming pool. The water reflects the sunlight and anything at the bottom of the pool, making the water look greener than it is. Keep in mind that leaving the debris in the water will encourage algae growth.

How to Fix

Follow this three-step process if you have organic matter in the pool:

  1. Scoop all of it out of the pool with a net.
  2. Get a pool vacuum to automatically remove small bits of debris from the water.
  3. Add a solar cover to the pool to prevent too much debris from getting into the pool.

Solar covers heat the pool and prevent evaporation and algae. The Sun2Solar Solar Pool Blanket comes in multiple sizes that fit almost any pool. It’s a 12-mil cover, making it one of the thickest and most durable selections available. You can cut the corners or let it stretch over the edges for complete debris protection.

Sun2Solar Solar Pool Blanket

Dirty Light Fixtures

If you have a dirty light fixture, the color will fill the whole pool whenever the light is on. For example, if there’s an algae bloom on the light cover, the whole pool will be the color of the algae. The good news is that you can clean or replace the dirty light fixture to fix this common problem.

How to Fix

Clean your pool’s light fixture with a soft sponge. Don’t use abrasive brushes because they can scratch the light. You can also use a chlorine tablet to clean the light, but make sure you brush off the excess chlorine with a sponge.


  • Jonah Ryan

    Jonah has worked for several years in the swimming pool industry installing and repairing equipment, treating pools with chemicals, and fixing damaged liners. He also has plumbing and electrical experience with air conditioning, ceiling fans, boilers, and more. When he's not writing for Temperature Master, he's usually writing for his own websites, and

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