Maintaining a pristine swimming pool involves more than just regular cleaning and chemical balancing. Stains and scale buildup can detract from the pool's appearance and affect water quality.

For pool service professionals, understanding stain and scale removers is important for providing excellent service.

Stain and scale removers are specialized chemical formulations designed to eliminate unsightly stains and mineral deposits from pool surfaces. Stains can arise from various sources, including algae, rust, metal, and organic materials, while scale typically results from calcium carbonate deposits due to hard water.

Composition Here are the primary classes of ingredients you might encounter: 1. Acids: Commonly used acids include muriatic acid and citric acid. These acids dissolve mineral deposits and help to break down stains. They work effectively on calcium buildup and rust stains.

2. Chelating Agents: These compounds bind to metal ions (like iron or copper) in the water, making them easier to remove. They help prevent stains from reoccurring by sequestering metals.

3. Enzymes: Enzymatic cleaners break down organic matter, such as oils, leaves, and algae, that contribute to staining.

4. Surfactants: These agents reduce surface tension, allowing the cleaner to penetrate more effectively into the stain or scale.

Stain and scale removers operate through chemical reactions that target specific types of stains and deposits: Acidic Action: When applied, acidic removers react with the alkaline minerals in scale, dissolving them and allowing them to be brushed away or rinsed off.

Chelation: Chelating agents encapsulate metal ions, preventing them from precipitating out of the water and forming stains. This action helps keep metals in suspension until they can be filtered out.

Enzymatic Breakdown: Enzymes in some cleaners break down organic materials leaving surfaces clear.

The effectiveness of stain and scale removers lies in their chemical composition. Here are the specific types of ingredients you might encounter:

EDTA

EDTA is a powerful chelating agent, meaning it binds with metal ions, making it particularly effective for removing metal-based stains in pools, such as those caused by iron, copper, and manganese. When EDTA is added to the pool water, it forms stable complexes with these metals, preventing them from precipitating and forming visible stains on pool surfaces.

EDTA has the added benefit of being relatively gentle on pool surfaces. Its chelating action can also help protect pool equipment by preventing metal deposits from building up and causing corrosion. EDTA is effective even in varying pH conditions, which makes it versatile in different types of pool environments.

While EDTA is effective at binding metals, it doesn’t work as well on calcium carbonate scale, so it is not the ideal choice for pools with high levels of calcium hardness. Additionally, EDTA can be costly, and it breaks down more quickly from chlorine than HEDP, another popular chelating agent.

HEDP (1-Hydroxyethylidene-1,1Diphosphonic Acid) (Etidronic acid) HEDP is both a chelating agent and a scale inhibitor. It binds to metal ions, like iron and copper, and sequesters them, preventing them from precipitating out of the water and forming stains.

HEDP is also effective at inhibiting scale formation, as it interferes with the crystallization of calcium carbonate, which can lead to hard, unsightly deposits on pool surfaces.

HEDP is highly effective at preventing scale formation and is often used in pools with high calcium hardness or high alkalinity, where scale formation is a persistent issue. Its dual function as a chelating agent and scale inhibitor makes it versatile, and it’s effective over a broad range of pH levels. Additionally, it has long-lasting stability in pool water, meaning it doesn’t need frequent reapplication. Like EDTA, HEDP can interfere with chlorine, reducing its sanitizing effectiveness.

This means careful attention to dosing is required to balance both stain/scale control and sanitation. Also, while HEDP is effective for preventing and treating scale and metal stains, it is not as strong at breaking down organic stains.

Citric Acid

Citric acid is a mild organic acid that is highly effective at reducing metal-based stains, especially iron stains, by reducing the metal ions and rendering them soluble.

When applied to metal-based stains, citric acid breaks down the stain, allowing the metal ions to be filtered out or sequestered with other chelating agents in the water.

Citric acid is an environmentally friendly option, as it is biodegradable and gentle on pool surfaces.

It is often used as a spot treatment for iron and copper stains due to its ability to break down rust stains effectively. Citric acid is also safe for vinyl and fiberglass pools, where more aggressive acids might cause damage.

Citric acid is only effective for metal-based stains and is not effective at preventing or breaking down calcium scale. Because it is acidic, it may lower the pool’s pH and require balancing afterward.

Ascorbic Acid

Ascorbic acid, also known as Vitamin C, is a reducing agent that effectively removes iron and other metal stains.

It works similarly to citric acid by reducing oxidized metals in pool water, such as iron oxide, which is responsible for brown or reddish stains. Ascorbic acid breaks down the metal ions, allowing them to be dissolved and either filtered out or kept in solution by a sequestrant.

Ascorbic acid is highly effective as a spot treatment for metal stains, especially on surfaces like vinyl, fiberglass, and plaster. It’s a gentle, non-toxic, and biodegradable solution, making it popular among pool techs looking for an environmentally friendly stain remover. Ascorbic acid works quickly, often producing visible results within minutes of application.

Ascorbic acid is not effective on calcium scale, as it primarily targets metal-based stains. Its reducing properties can also lower chlorine levels, so chlorine may need to be rebalanced after treatment. Additionally, ascorbic acid treatments may lower pH slightly, necessitating pH adjustments after use.

Oxalic Acid (Ethanedoic acid)

Oxalic acid is a stronger organic acid with a powerful ability to remove metal-based stains, particularly iron and copper stains, through its reducing and chelating action. It works by reacting with metal ions in stains, dissolving them into a soluble form that can be easily removed or sequestered in the water.

Oxalic acid is more potent than citric or ascorbic acid and can be particularly effective for stubborn stains on pool surfaces.

It is commonly used for spot treatment on plaster or concrete pools, where tough rust or metal stains are prevalent. It works well on surfaces that are more resistant to acid damage and provides fast, visible results.

Due to its strength, oxalic acid can be harsh on certain surfaces, particularly vinyl and fiberglass, and should be used with caution. It can lower pH more significantly than citric or ascorbic acid, so pH balancing is typically necessary after treatment.

Additionally, oxalic acid may interact with chlorine, reducing its efficacy temporarily.