Why did my pool turn green after adding pH up?

There are a few common reasons why your pool may turn green after adding pH increaser (also known as pH up). The most likely causes are:

Algae Growth

One of the most common causes of green pool water is an algae bloom. Algae spores are always present in pool water, but when the conditions are right, the algae can quickly multiply and turn the water greenish.

Adding pH increaser raises the pH level of your pool. Most pools function best when the pH is between 7.2-7.6. If the pH gets too high (above 7.8), it can allow algae to thrive. The high pH makes it harder for the chlorine sanitizer to effectively kill algae and bacteria.

So if your pool pH was already on the high side, adding more pH up could push it into the danger zone and trigger an algae bloom. The greenish color is caused by the millions of tiny algae cells suspended in the water.

Steps to Get Rid of Green Algae

To get rid of a green algae bloom:

  • Test and adjust the pool pH to 7.2-7.6 range
  • Shock the pool with chlorine or an algaecide to kill the algae
  • Brush walls and floors to remove dead algae
  • Run the filter continuously until the water clears
  • Determine and correct the underlying cause of the algae bloom

High Metal Content

Some tap water contains high levels of metals like copper, iron, or manganese. These metals can cause green staining in pool water.

When the pH increases, these metals become even less soluble in water. The metals may precipitate out of the water, resulting in greenish coloration, staining, or cloudiness.

Adding a pH increaser when the pool water already contains high metal concentrations can accelerate this process and make the green staining worse.

Correcting Green Water from Metals

To remove green metal staining:

  • Have a pool water test done to determine the metal concentration
  • Use a sequestering or chelating agent to bind the metals so they stay in solution
  • Add stainer and clarifier chemicals to clump particles together for filtering
  • Clean or replace filters regularly to remove metals
  • Use a stain & scale inhibitor to prevent metals from precipitating out

Improper Use of pH Increaser

Adding too much pH increaser at one time can also cause the water to turn greenish or cloudy.

When excessive amounts of pH up are added, some of the chemical may not dissolve fully and can settle on the bottom or walls of the pool.

Undissolved granules or powders of sodium carbonate (the active ingredient in pH increaser) may have a light greenish tint to them that can be visible in the water.

Too much pH up can also disrupt the water balance and chemistry, reducing the effectiveness of sanitizers and leading to algae growth.

Fixing Problems Caused by pH Increaser Overdose

To correct issues caused by adding too much pH increaser:

  • Test pH level and adjust to proper range with acid (pH down)
  • Turn on filter and pumps to circulate the water for 24 hours
  • Use pool brush to scrub walls and floor to dissolve deposits
  • Backwash filter to remove excess particles
  • Shock pool with chlorine to prevent algae growth
  • Add clarifier to help particles clump together for removal

High Total Alkalinity

Total alkalinity (TA) refers to the amount of alkaline buffers present in pool water. These include carbonates, bicarbonates, and hydroxides.

High TA provides excess buffering capacity that makes adjusting the pH difficult. The pH can easily get too high and fluctuate out of the ideal range.

Additionally, rapid pH bounce can occur when the TA is high. This is where the pH drops rapidly after increasing it. High TA causes the pH to be unstable and difficult to maintain in range.

When pH up is added to water with very high TA, the pH may spike well above ideal levels. This allows algae and metals to precipitate out, turning the water greenish.

Managing Total Alkalinity

To lower high total alkalinity levels:

  • Have water tested by a pool professional to determine current TA
  • Dilute the water by partially draining and refilling the pool with fresh water
  • Use an alkalinity decreaser chemical according to label directions
  • Confirm TA is in 80-120 ppm range after making adjustments

Presence of Copper Algaecides

Some types of algaecide products contain copper compounds like copper sulfate or chelated copper. When used properly, the small amount of copper in these products can kill algae.

However, under the wrong conditions, these copper algaecides can end up causing a green water problem:

  • High pH – Copper becomes much less soluble at pH above 7.8
  • Low alkalinity – Lack of sufficient buffers causes rapid pH fluctuations
  • Buildup of copper – Frequent algaecide use leads to accumulation of copper in the water over time

If pH up is added when copper concentrations are already approaching the precipitation point, it can push the water into an oversaturated state. This results in the excess copper precipitating out as a light greenish-blue stain or turbidity.

Dealing with Green Water from Copper Algaecides

To resolve a green pool caused by copper algaecides:

  • Stop adding copper-based algaecide
  • Test and adjust pH and alkalinity to proper levels
  • Use chelating or sequestering agent to bind copper
  • Use vitamin C or sodium thiosulfate to convert copper to a more soluble form
  • Run filter for extended time to remove precipitated copper particles

Incorrect Type of pH Increaser Used

There are a couple different types of chemicals used for increasing pH in pools:

  • Sodium carbonate (soda ash)
  • Sodium bicarbonate (baking soda)

Using the wrong type can result in pooling issues when you add more pH up.

For example, adding baking soda to raise pH when the total alkalinity is already too high can cause a spike in TA. And conversely, adding soda ash when the TA is low can rapidly lower the TA.

When an improper balance between pH and TA occurs due to the wrong pH increaser being used, unstable pH levels result. Rapid pH fluctuations allow algae and metals to come out of solution, producing a greenish colored pool.

Choosing the Right pH Increaser

To avoid issues, select pH increaser type based on total alkalinity level:

  • Use soda ash if TA is low (below 80 ppm)
  • Use baking soda if TA is high (above 120 ppm)

Test TA and pH regularly and adjust with appropriate chemical type in small doses to maintain proper balance.

Presence of Yellow Algae

In rare cases, adding pH up can induce growth of a type of algae called yellow algae or mustard algae.

Unlike green algae which prefer higher pH, yellow algae thrives in low pH environments. It tends to appear when the pH drops below 7.2.

However, sometimes drastically increasing pH can shock yellow algae and cause it to bloom briefly before dying off. The dying algal cells will turn the pool water greenish temporarily.

Additionally, if there are already some cells present, a spike in pH can disrupt the water chemistry enough to allow limited growth and reproduction of yellow algae.

Removing Yellow Algae

To get rid of yellow algae:

  • Adjust pH to 7.2-7.6 to prevent further growth
  • Shock pool with chlorine or algaecide specifically for yellow algae
  • Brush walls and floor thoroughly
  • Vacuum up dead algae
  • Clean filter to remove all algal cells
  • Maintain proper sanitizer residual

Preventing Green Water After Adding pH Increaser

To help prevent your pool from turning green after adding pH up, follow these tips:

  • Test pH, TA, and sanitizer levels before adding any chemicals
  • Add pH increaser in small increments, allowing time for it to dissolve and circulate
  • Don’t let pH rise above 7.8 or fall below 7.2
  • Maintain proper total alkalinity level based on pH increaser used
  • Shock pool regularly to control algae and prevent buildup of metals
  • Closely monitor copper concentration if using copper algaecides
  • Brush walls, steps, floor after adding pH up to evenly distribute
  • Change or clean filters as needed to remove precipitants
  • Watch for signs of algae growth and treat quickly


Green pool water is never a welcome sight. But with some troubleshooting and water chemistry adjustments, you can clear up the green and get your pool looking crystal clear again.

Be sure to test pH, TA, and sanitizer levels regularly. Only add pH increaser when needed in small amounts. Maintain proper balance of chemicals and run filter adequately to prevent algae growth and metal precipitation. Handle any underlying issues with algae or metals quickly.

Knowing the right steps to take when you notice green water will help resolve the problem fast and get your pool back to being that beautiful backyard oasis.

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