Swimming pool water with a high pH (typically above 7.8) can cause chemical imbalances. When the pH is elevated, it can reduce the solubility of metals like iron, copper, and manganese that may be present in the pool water. These metals are often introduced through sources like inferior metal-based algaecides, corrosion from pool equipment, or even through fill water that contains trace amounts of metals.

At high pH levels, the solubility of these metals decreases, leading them to “plate out” or precipitate from the water. When this happens, the metals solidify and form insoluble compounds that attach to pool surfaces, such as the walls, floor, and tiles. This results in the formation of stains, which are typically characterized by a reddish-brown (iron), greenish (copper), or dark purple-black (manganese) colour. These stains are not only visually unappealing, but they can also contribute to scaling and clogging of pool filtration systems if not addressed.

The Role of Acidic Chemicals in Metal Stain Removal

To reverse the staining caused by high pH and metal precipitation, acidic chemicals are used to dissolve the metal compounds. Acidic chemicals, such as Lo-Chlor’s Multi Stain Remover, lower the pH level of the water and create an environment that allows for the re-dissolution of the metals that have precipitated out of solution.

The process of using acid to remove metal stains works as follows:

Lowering the pH: By adding an acidic chemical to the pool water, the pH is lowered, which increases the solubility of the metals that had previously precipitated out. This helps to break down the metal compounds that have formed on the pool surfaces.

Dissolution of Metal Stains: Once the pH is sufficiently lowered, the acidic solution interacts with the metal stains, breaking them apart into dissolved ions that can be reabsorbed back into the pool water.

Any metal stain treatment is best conducted in the winter months, the reason behind this is that to effectively complete the stain treatment, the chlorine level in the pool needs to be lowered. This is because the Chlorine increases the PH and combats the stain treatment process. You can learn more about how chlorine production and chlorine cause the PH to increase in our previous Tech Talk.

The neglected steps 2 & 3:

Treating the metal stain in a swimming pool with an Acidic compound is only the 1^st step in treating the metal stain. Once the metals have been dissolved and reabsorbed into the water there is still the risk for them to plate out or precipitate again if left in the water.

The next step in treating the metals is to use a sequestrant agent such as Lo-Chlor’s Aquaguard CSM or Metal Solution. Sequestrants, also known as chelating agents or metal sequestering agents, are chemicals that bind to metal ions in the pool water, forming stable, water-soluble complexes. These complexes prevent the metals from precipitating out of the water and depositing onto pool surfaces. Essentially, sequestrants “trap” the metal ions, keeping them in a dissolved state and preventing them from reacting with other chemicals or materials in the pool that could lead to staining.

Now that the Metals are “trapped” its time to remove them from the water. If the pool has a cartridge filter, this will naturally happen with running the system and cleaning the cartridge element out every couple of days. With a Media or sand filter you will need some help to reduce the filtration to a fine enough level and help capture the dissolved metals. This is where Lo-Chlor’s Filter aid and metal remover comes in handy. Filter aid and metal remover is a fibre-based compound added to the sand filter. Fibre-based compounds have a high surface area, which provides more contact points for metal particles to be captured. When added to the sand filter, the fibres coat the sand grains, creating a more effective filtration bed. This enhances the sand filter’s ability to trap finer particles that would normally pass through the filter. Such as Metals which are often too small to be effectively captured by traditional sand filters. The fibre-based compound acts like a “scaffolding,” providing tiny spaces for the metal particles to become trapped. The increased surface area allows these small particles to stick to the fibres, preventing them from recirculating back into the pool water. Be sure to back wash the filter soon after (usually 24-48 hours) as using a fibre-based compound will increase the pressure in the filter.

Preventing metal staining in swimming pools involves a combination of proactive measures to control metal content, maintain proper water chemistry, and enhance the filtration system. Regular use of metal sequestrants, monitoring metal levels, proper pH control, and effective filtration can help reduce the risk of stains caused by metals like iron, copper, and manganese. By implementing these strategies, pool owners can maintain clear, stain-free water and protect their pool surfaces from metal-related discoloration and damage.