Early warning signs
As scale forms on the ECG’s cell plates, pool owners may observe small white flakes coming out of the pool returns or accumulating on the pool floor. They may also notice an unusual reduction in chlorine levels or difficulty maintaining chlorine, without other factors such as heavy rain or high bather load.
The following is a typical scenario. When scale accumulates on the ECG cell plates, chlorine production is hampered, and pool water begins to appear hazy. Testing confirms low chlorine levels, prompting most pool owners to turn up the ECG setting or pump time to increase chlorine production. When the new settings fail to solve the problem, pool owners inspect the cell and find scale. Some kinds of scale are visible, such as calcium carbonate; other kinds, such as calcium phosphate, are more difficult or even impossible to see.
Fortunately, once scale is confirmed by a visual inspection of the cell, it can be removed by washing the cell plates. The first step is to remove the ECG cell from the system, which is a relatively simple process. With the cell now accessible, try using a low-pressure hose to rinse off the plates. This will remove any large chunks of scale and may actually clear up the majority of the problem.
If more washing is needed, diluted muriatic acid (hydrochloric) can be used. Soak the cell for 15 to 20 minutes in a solution of four parts water to one part muriatic acid. This will remove most scale from cell plates; however, it also wears away the protective plate coating over time. Preventing scale—and minimizing the need for muriatic acid washings—will extend the ECG’s life.
Preventing scale
Most ECGs have an average lifespan of 10,000 hours, or between five and seven years. The lifespan of an ECG is determined by the amount of ruthenium oxide coating that is applied to the titanium cell plates. To prevent scale from shortening this lifespan, most ECGs incorporate reverse polarity. Since scale only forms on the cathode, the ECG will automatically reverse its current every two to three hours, so the anode becomes the cathode and vice versa. This allows scale to form uniformly on each terminal. Also, each time the polarity reverses, a bit of scale is dislodged.
While it helps combat the problem, reverse polarity is not a perfect scale prevention technique. It takes a toll on the ECG cell plates, because each time polarity reverses, a small amount of the ruthenium coating is lost. As such, proper care and maintenance is needed to further prevent scale. The following are some basic recommendations for scale prevention:
Use high-quality salt low in scale-forming minerals
Depending on how and where it was made, salt may contain naturally occurring minerals that can contribute to scale. Mined rock salt, which should never be used in saltwater pools, has the highest degree of inorganic contaminants and scale-forming minerals, including calcium, phosphate, sulfate and silicate. Solar salt, which is also not recommended for saltwater pools, may contain scale-forming minerals and large amounts of organic contaminants that can cause cloudy water and chlorine demand in the pool.
Mechanically evaporated varieties are best for saltwater pools, since the production process usually results in the purest kind of salt, with minimum amounts of both scale-causing minerals and other contaminants. However, the quality of mechanically evaporated salt can vary depending on the geographic location of the salt mine; despite the production method, some mechanically evaporated salts may still contain high levels of contaminants.
Ask suppliers to verify their manufacturing method and level of contaminants in the salt used. They should be able to guarantee the salt’s quality or provide a product specification sheet showing the level of minerals present.
