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.
