What Is The Difference Between Salt Water, Mineral and Freshwater Pools?
"What is the difference between salt water, mineral and freshwater pools?" If you are unsure, you are not alone! There plenty of claims out there offering "low salt", "salt free" and "chlorine free" options to sanitise your pool with equally big differences in the costs to buy and run the systems over 5 years. Spoiler alert! Even "chlorine free freshwater pools" have chlorine despite what the box says. Any pool, including DIY fibreglass pool kits, can be salt water, mineral or freshwater. Read on to understand the pro's and con's of each option including costs.
Before we look at the different the options, let’s start with why you need chlorine in your pool water. Chlorine kills the bacteria, algae and other yuckies (highly technical scientific term) that can be in your pool. It's why chlorine is in our tap water and usually in bleach too. It keeps your water sanitised and safe to swim in.
All pools need some form of chlorine or sanitising agent. The main difference between the systems is how chlorine is produced and the amount of chlorine needed in your pool water to do the job to meet Australian Standards. Let's also clear up another misunderstanding - no matter the system you use, there is no getting away from monitoring and testing your pH, water hardness and calcium levels.
There are four systems to chlorinate your pool - manual chlorine, salt water, mineral water and freshwater.
Chlorine Swimming Pools
Chlorine can be added directly to your pool water either as a dissolvable tablet, a liquid or in granular form. If you used to see an adult throwing strong smelling stuff from a bucket into your pool every other day in summer, you had a manually dosed liquid or granular chlorine pool. As it is a manual process, the challenge is maintaining a stable level of chlorine. When a dose is added, chlorine levels peak and then slowly reduce until more is needed. You might remember said parent saying "Don't swim in the pool for an hour, I've just put in chlorine" and then you promptly dived in 10 minutes later.
The biggest complaint about manually chlorinated pools is the strong smell, faded bathers/togs/swimmers and skin feeling dry after a swim and a bit smelly. Swimmers with sensitive eyes or eczema are usually not big fans. You will also need to add stabiliser. Why? UV light from the sun often kills chlorine faster than it can be produced by your chlorinator. The solution is to add a chemical (cyunuric acid) called stabiliser which acts like a sunburn cream for your pool water and protects your chlorine.
With kids in the pool every day in the warmer months, daily chlorine testing and dosing is usually needed. As it is a manual system, us Aussie blokes can tend to go with the "I'm not quite sure how much I need to add, so I'll throw in a little extra just to be safe" approach. Perfectly reasonable thinking in my mind until the kids start complaining about there being too much chlorine in the water!
Recognising the short comings of manually chlorinating a pool, salt water chlorinators were invented decades ago. Tap water doesn't contain salt (sodium chloride) so you need to manually add salt into your pool water around every 4 to 6 weeks on average in warmer months for this system to do it's job.
Salt water chlorinators have a salt cell that uses electrolysis to convert the salt in your pool water into chlorine. The salt cell produces a continuous bacteria-killing supply of chlorine while your pool pump is running. It is like being the manager of your own chlorine factory without ever having to touch a bottle or tablet of chlorine. Your pool water will feel softer without the strong chlorine smell as chlorine levels don’t peak and trough like a manually dosed pool. This is why almost all backyard pools bought in the last 20 years are salt water pools.
Pool salt is cheap and normally can be bought in 15kg and 20kg bags. You will spend around $100 to $300 on salt per year depending on your pool size and how much water you are topping up each week (meaning if each bombie competition requires a 1,000 litre top up of water, you will use more salt and chemicals maintaining your water sanitisation).
Your pool will not feel and taste like the ocean water as the salt concentration needed is 90% less than the ocean. Depending on your pool size and whether you are in a warmer State like Queensland or cooler State like Melbourne, your pool will need between, on average, 15grams and 25 grams of chlorine per hour to meet Australian Standards for water quality. Chlorine is drying on the skin so a swim in a salt water chlorinated pool can leave you feeling like you need a shower when it's time to hop out of the pool. As chlorine is present, you will need to add stabiliser as well.
As salt water chlorinators are fully automatic you need to keep less of an eye on your chlorine levels compared to a traditional “add the chlorine in manually” pool. We humans can be a little on the lazy side at times which means we are tempted to set and forget. You will still need to check your pool chlorine levels regularly. Too much chlorine can damage your pool and pool equipment and too little will invite an algae bloom.
The initial purchase price will be between $1,000 and $1,800 for a basic chlorinator and salt cell. The salt cell will need to be replaced every 3 to 5 years and will cost between $300 and $600 depending on your brand and model.
Mineralised Swimming Pools
The solution to reducing the drying feeling of a salt water chlorinated pool is to add potassium, magnesium and borates. Potassium is a natural moisturiser. Magnesium gives your water a soft, silky feel (grab magnesium bath salts and jump into your bath to test drive how it feels) and also acts as a natural sanitising agent. Subsequently, a mineral pool requires 40% less chlorine than a salt water chlorinated pool. Borates is a mineral often found in hair conditioner and over the counter eye drops for red eyes. Borates reduces eye irritation from swimming and prevents your hair from needing a wash after a swim.
Us humans absorb around 400ml to 500mls of pool water per hour of swimming until we get water logged (otherwise known universally by kids as "granny hands"). The benefits of magnesium on hair, skin and muscle health are well established and plenty of swimmers prefer to be absorbing minerals rather than chemicals. Check to make sure the minerals are food grade so you know you are getting the highest quality and concentration for your hard earned money. The idea of minerals from the "Dead Sea" is pretty enticing as it sounds so natural. Being natural is the issue. The quality and concentrations vary with every bag as it is naturally produced. Australian farmed food grade minerals provides a more consistent product.
Adding Magnesium and Potassium to your pool often increases water hardness. Quality pool minerals will include Boron which is a natural water softener which helps offset the higher hardness. If Boron is not present, you will need to add a chemical softener. With lower chlorine levels, you will be using less stabiliser as a trade off to adding a softener.
You can mineralise your pool using the standard salt water chlorinator. Your mineral mix will likely be 30% salt, 5% Boron and 65% Magnesium and Potassium. The lower salt content is sufficient for your salt cell to produce the reduced amount of chlorine required in a mineralised pool. This is the lowest cost way to mineralise your pool as you don't need to replace your salt water chlorinator.
Or, you can install a chlorinator that produces chlorine from the Potassium present in the water. These chlorinators will often promote your pool as being "salt free". What this really means is sodium chloride (salt) free. Potassium is a salt and the chlorinator still has a salt cell. It works the same way as a standard salt cell. However the salt cell converts the Potassium salt into chlorine instead of sodium chloride. These chlorinators will cost between $2,500 and $3,100 to purchase. The salt cell will need to be replaced at the 5 year or so mark and will cost between $600 and $800 to replace. The mineral blend will usually be 30% Magnesium and 70% Potassium.
When first adding minerals to a salt water pool or the pools first fill after installation, the cost of the minerals will be between $500 and $1,200 depending on the size of your pool. A rule of thumb is 40kg of minerals per 10,000 litres of water. You will need to top up your mineral levels as you would a salt water pool. On average, this will be a 10kg bag every 8 to 12 weeks costing around $30 to $40 per bag.
Freshwater Chlorinated Swimming Pools
You might know these as a copper sanitised, bionised, chlorine free or freshwater pools. They are all talking about the same method of sanitising your water. The promoted advantage of a freshwater pool is no chlorine and very low or no chemicals. Sign me up you say! Let's use some freshwater to cool those jets. There is a lot to like about freshwater chlorination systems however there are some drawbacks.
Freshwater chlorinators use Copper and Silver anodes to produce bacteria and algae spore killing ions. Silver ions kill bacteria and Copper ions kill algae spores. Sounds a little Star Trek doesn't it? "Captain, ionise those Klingons!" With no chlorine being produced, stabiliser isn't needed and ions are not affected by UV light. Other chemicals like softener are not normally needed and certainly no salt.
Ion's die as soon as they come into contact with bacteria or spores in your water which means they last as long as a sneeze. Australian Standards requires your pool water to maintain a residual level of sanitising agent when your chlorinator and pump isn't running to keep up the fight against bacteria and algae. With our ion friends having a glorious but short life, freshwater pools don't have a residual reading which means your pool is not compliant with Australian Standards. The solution is either run your chlorinator and pump 24 hours a day without turning if off or manually add some chlorine. Early versions of these systems also had problems with the Copper ions staining the pool surface in fibreglass and concrete pools leading to some pool manufacturers refusing to install these systems.
Around 10 years ago some clever boffins came up with hybrid freshwater model that solved both of these issues. By adding a chlorine oxidiser to the Copper and Silver anode system, the hybrid freshwater chlorination system was born. The chlorine oxidiser runs off very, very low levels of salt which produces just enough chlorine to meet the residual chlorine level required by the Australian Standards when the pump is off. How much salt? About 7kg for every 10,000 litres when first setting up which is virtually nothing. How much chlorine? About the same amount that is present in Australian drinking water which is normally very, very low and with no smell. With the addition of chlorine, the volume of Copper ions required is reduced to a level that doesn't stain pool surfaces.
The easiest way to know how a hybrid fresh water pool feels is to have a shower and see how your skins feels once you've towelled off. As you are not adding chemical stabiliser and water softener, your pool water is a very low chemical pool that doesn't have any drying effect that chlorine and salt water chlorinated pools have. Nice! If you have a media filter, you can discharge your dirty filter water straight onto your lawn or garden bed. Salt water and chlorine pool dirty water needs to discharge directly into a sewer line.
To purchase a hybrid freshwater chlorinator will cost you between $3,600 and $4,200. The anodes generally have a 2 year life and cost around $400 to replace. The oxidiser isn't cheap at around $1,000 and needs to be replaced around the 5 year mark.
There is a good reason why the majority of pools sold in Australia are salt water chlorinated pools. They are efficient, cost effective to buy and maintain and are liked by the pool buying public for their ease of use. If any regular swimmers in your pool have skin sensitivities like eczema or other muscle related challenges, mineralising your pool is going to make a noticeable difference to your pool fun and how you feel after a swim. If this isn't you, mineralising is pure personal preference and is a good middle ground between salt water and freshwater systems. The hyrbid freshwater system is the Rolls Royce option. There is no science to suggest any noticeable health benefits so again, it is pure personal preference for those with the budget to pay the premium to buy and run the system.
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About The Author
My wife and I grew up playing in swimming pools. Our daughters learnt to swim in our backyard fibreglass swimming pool. There is nothing quite like hearing kids splashing about and giggling. As pools do, our pool became a social magnet for friends, family and neighbours which we loved. Helping customers to have their own pool and saving customers thousands on their pool and equipment is the best job in the world.