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Guest Column - October 2010

Pool / Aquatics

Failing Salt Generators
The Phosphate Connection

By Terry Arko


Salt generators have gained in popularity recently, but the technology goes back to 1800, when scientists discovered the technology of splitting molecules in a solution using what is called electrolysis. Salts like sodium chloride or sodium bromide are used in a solution that is subject to low-voltage electrical current and a pair of cells with opposing charges. One cell, the anode, contains positive charges, and the cathode contains negative charges. Electrical ions flow back and forth between the two cells. When sodium chloride passes across these cells, molecules are split and chlorine gas is produced at the anode. Hydrogen gas is produced at the cathode. Salt generators produce hydrogen gas, chlorine gas and a solution of sodium hydroxide. When salt generators are working properly, they are continuously producing free available chlorine to proper set levels.

What Happens When Salt Generators Fail?

When a unit begins to fail, it will not produce sufficient free chlorine to keep up with demand. There are numerous reasons for failure, including dirty or calcified cells that need to be cleaned, no power to cells, or insufficient levels of salt in the water. But, there is one main factor to consider first when a salt chlorine generator fails: the presence of phosphates in the pool water.

When levels of phosphate exceed 500 ppb, the unit can cease to produce enough free available chlorine to keep up with demand. Most manufacturers of salt chlorine generators will confirm that when there is a problem with production of free available chlorine a phosphate test is recommended. If the phosphate levels are near or over 500 ppb, a phosphate removal treatment is advised.

A typical example of salt generator failure is what happened recently to Steve White, owner of Underwater Pool Masters in Massachusetts. He installed a new salt chlorine generator at an outdoor commercial swimming pool, but could not get a decent chlorine read for over two weeks after the installation. "The situation was such that we ended up having to continue to shock the water to sanitize the pool until we could make sure the new salt generator was producing the optimum chlorine levels," White said.