Secondary testing can keep metal content under control

by Sally Bouorm | June 1, 2011 9:16 am

16577705_edited-1 — If metals are suspected to be present in source water, it must be tested before making any other adjustments to water chemistry.

By Joe Sweazy

How do pool professionals deal with cloudy, discoloured water? How about surface stains and rusty metal parts or complaints from swimmers whose hair is turning green, even when the water seems to be properly balanced. These and other symptoms can drive pool managers crazy—and they can all be a result of elevated levels of common metals in swimming pool water.

Where do metals come from?

Copper and iron are the two most common problem metals for swimming pools and spas. While they are essential micronutrients in every adult’s diet, we try to reduce or eliminate these unwanted metals in swimming pool (and, occasionally, spa water).

Source water

The most common origin of copper and iron in pools and spas is the source water itself. Water percolating through soil and rock can dissolve minerals containing copper or iron; this contaminated water eventually makes its way into wells or other reserves.

Pipes and plumbing

Municipal water supplies typically have lower levels of unwanted metals, but even if well water isn’t used to top off the pool, metals can still make their way into the water, often via old, dissolving pipes and plumbing. This and other metal equipment in your pool can corrode, particularly if the water’s pH or calcium hardness level is too low.

Chemicals and systems

Some algaecides used for pool maintenance contain copper as an active ingredient. Also, copper is commonly used in increasingly popular mineral purification systems for pools and hot tubs; the metal often plays a part in these systems because of its sanitizing abilities. As such, if a mineral purification system is being used, copper levels must be kept low (at or below 0.2 parts per million [ppm]). Otherwise, it can form scale deposits or stains.

What do metals do to the pool?

Once metals have found their way into a pool, several water chemistry factors can contribute to discolouration and scaling. High total alkalinity (above 180 ppm) can promote stains and scale formation from metals; a pH above 7.8 can also cause these problems. In addition, oxidation can occur, drawing metals out of the solution and ultimately creating worse problems.

Explaining oxidation

672367 — When a metal compound is exposed to air, it can oxidize into a colourful, solid form.

When a metal compound is exposed to air, it can combine with oxygen, creating a new form of the metal. In deep wells or piping systems, where the oxygen content is low, the water containing copper and iron is clear and colourless. Therefore, the water from the tap containing these metals not seem suspect. However, when exposed to air for some time, the metal content can oxidize into a colourful, solid form.

For example, oxidation changes iron in the water into a yellow or reddish-brown solid, while copper tends to take on a blue or blue-green shade. When these metals settle out of water in their solid form, they cause stains and rust on pool surfaces, fixtures and equipment. Smaller particles remain suspended in the water, causing a cloudy, discoloured appearance that is less than appealing to potential swimmers.

7636300 — When these metals settle out of water in their solid form, they cause stains and rust on pool surfaces, fixtures and equipment.

Exposure to air is just one method by which oxidation can occur. Another more powerful oxidizer is often responsible for faster metal precipitation—the free chlorine used to sanitize swimming pools. The qualities that make chlorine great for destroying unwanted debris and contaminants can also set metal staining and scale formation in motion.

The free chlorine and available oxygen in your pool will speed up the rate at which elevated levels of copper and iron oxidize. Water that looked clear and perfect from the tap then becomes cloudy and discoloured with a primary shock dosage. Even if already-chlorinated pool water is simply topped off with fresh water containing metals, there is potential for a metal problem.

This is not just limited to chlorine oxidizer. Other sanitizers or shock agents may also help oxidize metals into forms that cause stains and scale buildup.

How are these problems treated?

If metals are suspected to be present in source water, it must be tested before making any other adjustments to water chemistry. The metal content might need to be reduced first in order to avoid stains, scale and cloudy water. It is important to do this before adding any oxidizer such as chlorine, since, as previously discussed, it can oxidize metals into a more problematic form.

If using a copper-based algaecide or a mineral purification system, water will need to be tested frequently. Copper levels should be kept below 0.2 ppm or more serious problems than algae may occur.

Dip-and-read test strips can provide a quick analysis of the metals in solution, indicating iron and copper levels accurately in seconds. Liquid drop kits or test tablets are also available to detect low, but potentially harmful levels of iron and copper. All of these methods can also provide reliable analysis in a short enough period of time to be used at poolside.

With occasional testing in problem waters, keeping metal levels under control should be relatively simple. If detected, the typical way to eliminate or reduce the metal content in your water is with a sequestering or chelating agent. A sequestering agent is a chemical compound that can bind the metals into large particles. Once it does its work, the filter can intercept the large particles containing the metals, allowing them to be backwashed out. A chelating agent will work to suspend the metals back into solution. This method may not be a permanent fix and several doses of the agent may be needed. If metals are a recurring problem, weekly dosage with metal remover may be the best defence against potential metal-related problems.

Any metal treatment chemicals will work more efficiently if the pool water is properly balanced for pH, alkalinity and hardness. Therefore, these levels may need to be adjusted before adding metal-removing chemicals. Otherwise, the chelating agent will have to work harder to do its job, meaning operators will have to add more of it and spend more money. Again, be sure not to add any oxidizers, such as chlorine, until the metals have been treated. Always follow the manufacturer’s directions with this or any other pool and spa chemical for best results.

Testing and prevention

3304283 — Inexpensive testing methods can serve as insurance to prevent rusty iron contaminated water from building up in pools.

Metals may be a menace, but they can be easily controlled once you have identified the problem and the source. Regular testing and maintenance will prevent significant issues and costly and time-consuming clean up or repairs to rusty equipment. Inexpensive test strips or other testing methods can serve as insurance to prevent metal buildup and avoid much more expensive repairs.