These days, many in-ground swimming pools use a salt-water chlorinator to keep the water clean and safe from nasty microbes.

The Pool Salt Meter at our local pool shop. Obviously, it does more than check dissolved salt levels - it also checks total dissolved solids. But it also costs more than $300 and, according to our friendly pool shop owner, " . . . costs a fortune to repair, too." We wonder why!

The chlorinator electrolyses the salt content of the water to produce sodium hypochlorite which then acts like normal "pool chlorine" to sanitise the water. Not having large amounts of chlorine in the water makes it much more pleasant and you don’t come out of the water smelling of chlorine. Nor will your eyes sting or your swimming togs become bleached.

However, for a salt-water chlorinator, there must be a minimum concentration of salt in the water for it to work correctly.

Just how much is needed depends on the brand and model of chlorinator but typically it is around 3000 to 4000 ppm (parts per million). If the salt concentration goes below the specified level, you must add some salt to the pool.

On the other hand, you should not add too much as that is simply wasteful and it might lead to accelerated corrosion of some of the pool hardware.

So how do you measure salt water concentration? Most people don’t even bother. They just take a sample of their pool water to the pool shop and ask them to test it (at the same time getting several other important pool chemistry factors checked). If it is below the specified level, this is the perfect opportunity for the pool shop to sell some bags of salt.