How salt water chlorination works in swimming pools

That is a brief explanation of how salt water chlorination works in swimming pools. Most people will know that that the best chemical for killing algae and bacteria in swimming pool water is Chlorine.Most people will know that salt is Sodium Chloride, a Sodium atom bonded to a Chlorine atom. Chemical Symbol NaCl.

Most swimming pool owners know that they have to regularly buy “Chlorine” granules and throw them in their pool to kill algae and bacteria to keep their pool water clean and safe to swim in. It gets used up and you have to go and buy more.

The more savvy pool owners will know that one of the types of  “Chlorine” they could use is actually Sodium Hypochlorite and when he adds it to water Hypochlorous Acid (HOCl) is formed and that is what actually kills stuff.  Sodium Hypochlorite sounds a bit like Sodium Chloride – salt. Well, it is close, but just putting salt in your pool will not kill bacteria  – you have to “hypo” it. To “hypo” it you have to add an Oxygen atom.  If you mix a lot of water (H2O) and little salt (NaCl) together and pass an electric current through it, greatly simplified, an Oxygen atom and a Hydrogen atom join up with a Chlorine atom and you get H + O+ Cl = HOCl, hypochlorous acid. Bingo! All bacteria are dead and lovely clean pool water. That really is just about all there is to salt water chlorination except read on because it gets even better.

Strictly speaking it is not Chlorine that kills bacteria or algae it is the Oxygen that does the killing by oxidising the bacteria, the same reaction as burning something. Burning, setting fire to and oxidising are all the same thing, either way the bacteria is dead. So the Hypochlorous acid gives up its oxygen atom to burn the bacteria and the chlorine atom goes back in to the water. That is until it finds its way back to the electrodes of the salt water chlorinator and re-forms in to HOCl again and goes off looking for more bacteria to kill. Self regeneration, a never ending supply of hypochlorous acid means you never have to add sanitising chemicals to your pool water again.

So it is not hard to see why salt water chlorination is an ever more popular way to sanitise a swimming pool. Just add salt to the water and fit a set of clever electrodes called a salt water chlorinator and you can have pristine clean pool water and no need to add sanitising chemicals ever again. The high electrical current between the electrodes will also kill any algea spores in the water so although the hypochlorous acid would have got them anyway the electrodes killing them off means you can lower the chlorine level down to about 0.5 ppm.

The pros and cons of salt water chlorination for swimming pools

The biggest and most obvious advantage of salt water chlorination is that you never have to add any chemicals to your pool ever again. Cleaning chemicals that is – chlorine, algicides, clarifiers will be a thing of the past. All you will need is pH balance chemicals now and then. No more pulling back the cover and finding the water has gone green since you last looked at it. Provided you don’t switch it off your salt water chlorinator will keep your water pristine clean all season.

The water will “feel” much nicer. This is a difficult concept to explain but the water will feel softer and more inviting. Because the salt content is much closer to that of your eye water, red eyes and eye irritation will be greatly reduced. Your fingers will not go as “wrinkly” due to the salt content and you will not come out of the pool smelling of chlorine.

So with pristine clean water forever and no chemicals what could possibly be the downside to salt water chlorination? Well, not much really. Despite what the manufacturers might claim, the water does taste salty. Not very salty,  at 10 times less salt than the sea it is not unpleasant, and after a few weeks regular users will get used to the taste and barely notice it at all.

The installation process involves putting a lot of salt in your pool. Eight 25kg bags for a 50m3 (11,000 gallon) pool. But at least you only have to do it once. You will need to keep a few bags of salt on hand because as you top up after backwashing or evaporation you will need more salt sooner or later.The biggest disadvantage is the cost. For a 12 x 24 pool a salt water chlorinator will cost about £850.00 and the salt will cost about £100.00.  That is about 10 years worth of chemicals but factor in never having to go out there and dose your pool, except for the pH now and then, and the pay back may well seem to come a lot quicker.