My pool water is green; why is that? It's fixable

Causes of green pool water

A tidy, well-kept pool in your backyard will always seem appealing. Don't panic, though, if you see a greening of the pool water—this is a regular issue for pool owners. You must be persistent, identify the root of the issue, and fix it. Algal blooms, an imbalanced chemical composition, and filtration system malfunctions are the main reasons. In the sections that follow, we'll examine the root causes of the issue, go over the part algae plays, talk about chemical imbalances and filtration issues, and give you the information you need to fix the issue and restore your pool to its former glory.

Filtration Issues

A green colored pool often has a faulty filtration system. If the filter is not working properly, it will not be able to effectively remove the tiny particles that give the water its green color. Improper filter settings, a broken pump, or a clogged filter may be the cause of this problem.

Here are some signs that a green pool problem is due to a filtration issue:

• The pool filter is either clogged, dirty or is not being cleaned/flushed regularly. If the filter is clogged, it will not be able to effectively remove particles and debris from the water.
• During the day, the filter pump is running for insufficient time or at insufficient flow rates. Due to insufficient filter run time, particles remain in suspension.
• Noticeable problems with the filtration system itself - leaks, cracks, improper assembly or the need to replace filter media.
• Debris clogged pump basket or pool skimmer basket preventing water from entering the filter.
• The pool has a very high level of dissolved solids that have accumulated over time due to insufficient backwashing or refilling.
• A tinge of green water color has remained despite the balanced water chemistry that you have applied and treated the pool.

Chemical problems

Another typical reason of green pool water is an improper chemical balance. While high pH levels can lessen the efficiency of the chlorine, which promotes algae development, low chlorine levels allow algae to flourish. Too much cyanuric acid can exacerbate the situation by interfering with free chlorine levels.

Some telltale symptoms that a green pool problem is caused by chemical imbalances or issues:

Low Chlorine Levels

One of the primary causes is low free available chlorine levels. The pool is cleaned using chlorine to stop the growth of algae. If chlorine drops too low (below 1-3 ppm), it allows algae to take hold, resulting in that green tint. Check chlorine with a test kit.

High pH Levels

If the pH gets too high (above 7.6), it reduces chlorine's effectiveness at killing algae and bacteria. The ideal range is 7.2-7.6. High pH, combined with low chlorine, creates a perfect environment for algae proliferation.

High Cyanuric Acid

Cyanuric acid stabilizes chlorine in outdoor pools, but excessive levels (over 100 ppm) can deplete active chlorine levels over time. This ties up the free chlorine needed to keep the pool clear.

Low Alkalinity

Alkalinity acts as a pH buffer. If it drops too low, it allows the pH to bounce around and become difficult to manage, indirectly impacting chlorine efficacy.

My pool is green, how do I fix it?

If your pool has turned green, the first step is to shock it with a high dose of chlorine to kill the algae.In order to assist the algae clump together and make it easier for the filter to remove, you might also need to apply a pool clarifier. Once the chlorine levels and pH are balanced, and the filter is working correctly, the green should clear up.

The type and strength of shock treatment can make a difference depending on how severe the greening of the pool is. Here are some considerations:

Mild Green Tinting

- For a mild green tint, a standard chlorine shock treatment at normal strength (following product instructions) may be sufficient to clear it up.

- Common chlorine shocks like calcium hypochlorite, lithium hypochlorite or dichlor can work for mild cases.

Moderate Green Water

- If the water has a more pronounced green color, a stronger chlorine shock treatment is recommended.

- Use shock products at maximum dosage based on pool volume. Double-shocking may be needed.

- Non-chlorine shocks like potassium peroxymonopersulfate can also be effective against moderate green algae growth.

Severe Green/Pea Soup

- For severely green, "pea soup" water, an extremely concentrated chlorine shock is required, often using cal-hypo shock at 2-4 times normal strength.

- In extreme cases, adding a metal-free algaecide along with the chlorine shock can help knock down stubborn algae blooms faster.

- Repeated shockings a few days apart may be necessary before the filter can clear out all the dead algae.

The stronger and more concentrated the shock treatment, the faster it can kill off larger algae blooms turning the pool green. But it's important not to over-shock beyond recommended dosages, as it can lead to excessive chlorine burn-off. Patience is required for very green pools.

Steps to clean a green pool

• Check water PH, chlorine and cyanuric acid levels.
• Set the PH in the recommended range (usually 7.2-7.6).
• Add high doses of chlorine to the pool (follow the preparation instructions).
• Add a pool clarifying agent to help collect algae.
• Turn on the filter constantly until the water is clear.
• Clean the bottom of the pool with a vacuum cleaner to remove any settled algae and debris.
  Use a handheld pool vacuum to remove settled debris and algae.
  Pay special attention to corners, ladders, and areas where the main drain is located.
  Cleaning may need to be repeated over several days.
• Monitor chlorine and pH levels and keep them at the proper levels.
• Replace the water if necessary.
  In serious cases, partial draining and refilling of water may be necessary.

Green pool water not algae

Excellent idea! The most frequent theory regarding green pool water is that it's caused by an algal bloom. But the green color might not be due to the formation of algae. Examples of "green pool water, not algae" include the following:

Mineral stains/tints:

High concentrations of dissolved metals, such as iron, copper, or manganese, can oxidize and turn pool water green or blue-green in color.

This is more typical in places where the water is contaminated with high concentrations of metals.

The pool's sides and floor are painted with metal, which gives the water a green hue. 

Pollen outbreak: 

When pollen counts are high, wind-borne pollen from trees and plants can gather in pools, turning the water a shade of greenish yellow.

Pollen is not always noticed while inspecting a pool for algae because it floats in clouds.

Organic Matter Tints:

When leaves, seeds, grass, or other organic debris break down in the pool, the water can get murky and turn a greenish-brown hue. This is not the same as a noticeable algal bloom. 

Water Reflection:

In certain situations, the green color is really the result of nearby trees or other landscape refracting at a specific angle off the pool's surface.

It might not be an algae issue if common algae treatment techniques like shocking, brushing, and vacuuming are ineffective in getting rid of the green tint. Green water issues unrelated to algae can be found and eliminated with the use of water filters and metal testing.

Pool is green and cloudy after shocking

A green pool may remain green and hazy even after it has been chlorinated. Although the validity of this occurrence may be questioned, there are a number of potential causes:

Dead Algae Still Present

Dead algae take time to vanish after being shocked in a pool. Live algae are oxidized and killed by chlorine shock, but the dead algae and debris still need to be filtered away, which is a laborious process. Until all of the dead algae is gone, the water will appear green and murky.

The filter is not working properly.  

After shock treatment, the filter won't be able to get rid of all the dead algae and debris if it isn't operating at maximum efficiency. The efficacy of water treatment can be decreased by clogged filters, pump issues, ripped filter screens, and incorrect disassembly.

High levels of dissolved solids.

Large amounts of dissolved solids and pollutants, including metals, dirt, and body oils, build up in pools over time. The water turns murky because they are suspended and agitated by an electric current. Chlorine finds it difficult to oxidize all pollutants due to the high solids content.

Algae Still Alive

In cases of severe, resilient algae blooms, a single shock may not have been potent enough to kill off all the living algae. Some hardier types like mustard or black algae require multiple shockings or algaecides.

If a pool remains pea-soup green and cloudy 24-48 hours after shocking, additional steps are likely needed like:

• Adding clarifier or flocculant to help the filter catch more particles
• Chemically cleaning or backwashing the filter 
• Raising chlorine levels and re-shocking
• Partially draining and refilling to lower solids
• Brushing walls and steps to dislodge algae

Getting a pool clear after a bad algae bloom often requires diligence and repeating steps until clarity is achieved.

Pool Is Green But Chlorine Is High

It may seem counterintuitive, but there are times when the chlorine level in the pool is high, but the water still looks green. Here are some possible explanations for this situation:

Cyanuric acid blockage

If the level of cyanuric acid (stabilizer) is very high above 100 ppm, it can “block” much of the free chlorine. This reduces the effectiveness of chlorine in disinfecting and preventing algae growth, despite the high levels in the test kit.

Chlorine Demand

Intense algae blooms or high swimmer loads in the water can result in a high chlorine/chloramine requirement to bind free chlorine. Total chlorine levels were high, but there was little free chlorine left to sanitize.

Problems with pH

If the pH level of the pool exceeds 8.0, the sanitizing effect of chlorine may be reduced. A high ph level greatly reduces the effectiveness of chlorine in controlling contaminants such as algae.

Filter problems

Clogged and inefficient filters cause chlorine to not circulate or filter properly. Algae can persist in the “dead zone” despite adequate chlorine levels elsewhere.

Biolayer /bacteria

Chlorine resistant bacterial colonies and biofilms can color the water green, and it is not always possible to eliminate this by simply shocking the pool.

In such cases, cyanuric acid levels are usually first reduced by diluting or draining/refilling as needed. Then shock again to the desired pH level, rinse the filter thoroughly, and make sure it is running at optimum performance. For chronic conditions, algicides may also help.

Pool Water Looks Green But Clear

The water in the pool may look green, but at the same time remain clear or clean. This situation is not always a serious problem, but indicates an imbalance that needs to be corrected.

Surface algae

A greenish tint can be caused by algae growing on pool walls, floors or steps rather than floating freely in the water itself. This type of algae attached to the surface can color the water green without causing turbidity.

Early algae blooms  

You may have observed the earliest stages of an algae bloom. The first small algae particles may give the water a green tint before it begins to turn cloudy and stain the water as the bloom develops.

High levels of dissolved metals

As mentioned above, excessive levels of certain dissolved metals such as copper and iron can cause the pool water to take on a greenish tint, but it will also be clearly visible at the bottom.

Pollen and landscape tints

Pollen in the air, debris in the landscape, or even reflected light from surrounding trees/plants can give a greenish hue to a clean, algae-free pool.

In conclusion, prompt resolution of this issue can avert the need for drastic control measures. In order to avoid and treat green pool water, it is essential to maintain the right chemical balance and filtration. Throughout the whole season, regular testing, cleaning, and maintenance will keep your pool looking its best.