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Facts and Myths about Calcium Hardness

As with every other aspect of water chemistry, calcium hardness also needs to be in balance to protect your pool surface from calcium formation, stains, or corrosion. Unlike pH and chlorine, the calcium level in most pools does not vary greatly over the seasons, so testing every few months is normally sufficient.  High or low calcium hardness can cause white staining on pool surfaces, etching, or discolouration. The trick is to maintain the calcium at the right level in between.


  • Pitting on concrete pool surfaces
  • Etching of pool surface
  • Dissolving of tile grout
  • Pitting on concrete pool surrounds


  • Cloudy water
  • Rough surfaces in pool
  • Clogged filters and reduced circulation
  • White ‘blotchy’ areas on pool surface

What about calcium hardness reducers?

Some inexperienced pool technicians believe that adding a ‘calcium hardness reducer’ will permanently lower the calcium level. This is simply not the case because the calcium isn’t actually removed from the water with these treatments. These ‘reducers’ work by using chemicals to bind up (or capture) the calcium temporarily.  While these treatments do reduce the effects of high calcium in the short term, after 4-6 weeks, the ‘reducer’ chemical is completely neutralized and broken down.  When this happens, the calcium is released from the chemical bond and then simply returns to the previous tested level.

Topping up pool
Photo Credit: Truitt's Water Service

Just adding tap or tank water will do the trick, right?

Topping up the pool with fresh tap or tank water will not slowly reduce the calcium level over time. Adding more water does not lower calcium hardness because as water evaporates into the air, the calcium is left behind in the pool. Remember, water evaporates but calcium does not! This means that calcium stays in your pool no matter how many times it is topped up. Concrete pools will also release some calcium into the pool water over time, particularly when the pool surface is new.

What if my calcium hardness is too low?  Isn’t that good?

The only way to permanently lower your calcium hardness level is to pump out (through backwashing or draining) a small amount of existing pool water and then refilling.  This works because calcium rich water is pumped out of the pool and then replaced with tap or tank water with very low levels of calcium.  Depending on where you live, most tap water in Australia has a calcium hardness of around 50ppm (Sydney water) while tank and rainwater contain no calcium.  Following this “drain and refill process” will lower the calcium hardness level permanently without chemicals!  If you live in a region that is known for ‘hard’ calcium or mineral rich water, then it may be an idea to have the calcium level of your tap water measured before starting this process. You don’t have to drain the entire pool to lower the calcium level. In many cases, replacing as little as 30-40cm’s of water will bring your pool back into the normal calcium range.

How do I adjust my calcium hardness?

If your calcium hardness is too low, it can be easily increased by adding calcium chlorite from your pool shop.  Adding calcium to your pool will increase the calcium level right away.  On the other hand, if the calcium hardness is too high, then we suggest pumping out some water from the pool and replacing it with tap water as mentioned above.  Exchanging the water using this method is inexpensive, permanent, and will also make the water feel a lot nicer to swim in.

If you don’t know your calcium hardness level, we suggest getting it tested as soon as you can.  If your pool shop is not equipped to test for calcium hardness, try another shop.  Because all surfaces can react with calcium, the calcium level is important to know (NSW Health).

Calcium reduction…the natural way.

One method that works to reduce calcium hardness is to pump out water using your pool cleaner or vacuum hose during periods of soaking rain when your pool is likely to overflow.  This method removes high calcium water from the bottom of the pool while at the same time, the rain refills it with fresh water that has no calcium at all.  Doing this several times a year can have a huge impact on the calcium level in your water and best of all, it’s free!

Calcium build-up on fibreglass pool
Calcium build-up on fibreglass pool

What about calcium in fibreglass pools?

Some pool shops are unaware that the recommended calcium level in fibreglass pools is often different to concrete pools.  Because of this, some pool shops will incorrectly advise customers to significantly increase the calcium level in their water.  This mistake happens because the water testing software used at pool shops is primarily designed for concrete pools (which are more common) rather than fibreglass.  Most concrete pools have a suggested range of 200-300ppm of calcium while fibreglass pools often have a lower suggested range.  To ensure that your water is at the right level, check the suggested calcium levels with your pool manufacturer. The pool shown here is from a client who had heavy calcium build-up on their fibreglass pool from poor water balance.  In addition to surface problems, excessive calcium in a fibreglass pool can clog salt cells, damage the heater, and obstruct pipework (Swim University).

Calcium hardness in MagnaPool systems

A common trap for inexperienced pool technicians and owners is understanding that unlike a typical salt pool, ‘total calcium hardness’ in MagnaPool also includes the ‘magnesium salts’ (used to run the MagnaPool system) as part of the total calcium reading. This means that in a pool water test, the high level of magnesium salts in the water will show as calcium.  For MagnaPool systems, 70% of the total hardness reading is actually comprised of magnesium salts rather than calcium.  Because of this, the actual calcium hardness reading for magnesium pools should be substantially higher than typical salt pools to compensate for the magnesium content in the water.  If your MagnaPool is running a measured calcium hardness of 200-250ppm, then your actual calcium level is too low and should be increased right away.  MagnaPool recommends a ‘total hardness’ level of around 800ppm compared to 200-300ppm for typical salt pools (MagnaPool).

Calcium lumps in swimming pool
Calcium lumps in swimming pool

How do I clear calcium lumps off my pool surface?

If you spot calcium lumps or blotches in your pool, please don’t alter your calcium hardness to try and fix this issue. Some people advise that reducing your calcium hardness will dissolve the calcium formation on the pool surface. This is not true. Maintaining the calcium hardness level at either extreme will only make the calcium formation worse, not better. The only way to treat calcium formation on a pool surface is to either use a calcium dissolving compound, or to drain and acid wash the pool.
If you have calcium lumps, streaks or blotches forming in your swimming pool, please feel free to contact us for further information. We can help you remove these without draining your pool water.

salt - magnified
Image of swimming pool salt under a microscope.

Contaminated salt leads to stained pools

Almost daily we receive telephone calls from distressed clients saying the following – “I got some cheap salt from my local hardware store and now I’ve got these ugly brown stains in my pool”.  Often, this brown staining becomes evident within hours of adding the salt to the water.  Many pool owners around the world face this issue. What are the key differences between bad salt and good salt and why does it matter to your pool? Let’s find out.

Good salt versus bad salt.  What’s the difference?

All salt has the same basic properties. However, the mineral, water and metal content that accompany pool salt can vary significantly from brand to brand.  For this reason, the quality of salt used in your pool has a significant impact on the volume of minerals and metals that are dissolved into your pool water over time. These minerals will later discolour and stain your pool interior, particularly if your pool water chemical balance is not maintained.

We all know that pool water evaporates over time. However, many pool owners are not aware that these minerals, metals and contaminates from salt do not evaporate even once dissolved in the pool. These minerals remain suspended in the water, even when the pool is topped up with fresh water. Using quality salt will significantly slow down this mineral accumulation in your pool.

How can I recognize poor quality salt?

There are 5 things that typically characterize poor quality salt.  They are as follows –

  1. Salt crystal size is large
  2. Salt is discoloured
  3. Salt is slow to dissolve
  4. Salt turns water murky when added
  5. Salt leaves brown stains on your pool floor

If the salt brand you are currently using matches ANY of the attributes in the list above then we strongly suggest trying an alternative.

What does good quality salt look like?

There are five things that characterize good quality salt.  They are as follows –

  1. Salt crystals are fine
  2. Salt crystals are fast dissolving
  3. Salt bag displays a purity level of at least 99.5%
  4. Salt is brilliant white in appearance
  5. Pool water feels soft and comfortable for swimmers

How much extra is good quality salt?

Most pools need around 10-12 bags of salt per year to maintain correct salt levels.  The cost difference between poor and high quality salt is around $4 per 40 lb bag.  This additional cost for quality salt is not significant.  On the other hand, the cost of removing stains caused from poor quality salt can sometimes be over $1000.00. From a financial perspective, cheap salt does not make any sense.

Most pool owners spend less than $120 per year on pool salt.  It is unwise to cut corners by using cheap salt when the consequences can be so costly.

There are times when inexpensive brands sell reasonably high quality batches of salt.  However, less expensive brands need to source lower grade salt in order to meet the low prices some consumers demand.  Therefore, the chances of purchasing a contaminated batch of salt is generally higher with less expensive brands. High purity, fine salt is in demand in several industries and simply costs more to buy.

Another thing to be aware of in terms of cost is that salt is sold by weight.  Some low cost brands will buy moisture rich salt at a lower price in order to undercut their competitors.  Because moisture is not desirable in salt, it is sells for a lower price.  This means that if the salt moisture levels are high then you’re actually paying for water rather than salt! Remember, salt is sold by the total bag weight, not by the actual amount of pure salt in the bag. Therefore, the actual amount of pure salt you have in your salt bag will depend on the quality of the salt, not the total weight of the bag.

Although no brand or batch of salt is 100% pure and completely free of all contaminates, high quality brands generally have better quality control and more accurate measures to monitor mineral content.  When added correctly to your pool, good quality salt saves you money over the life of your pool and will actually cost you less in the long term.

If your pool has salt staining that you cannot remove, please feel free to call The Pool Stain Removers today.  We can help you remove salt stains without draining your pool water.

Do you have any comments or experiences with salt that you would like to share?  We look forward to hearing about them via the email address on our website.

salt stains
Our client in Melbourne, Australia placed a full bag of salt on the steps of their pool and left it to dissolve overnight. The next morning the steps and the entire pool had a horrible brown stain caused from contaminates within the salt.


Colour, crystal size and purity –

Customers upset and complaining about staining from cheap pool salt –

Adding salt to your pool correctly –

Salt quantity needed per year –

Long term benefits of using good quality salt –

Salt graded by water content –

There are 6 reasons why your pool water may be cloudy. They are:

  • High pH
  • High Calcium Levels
  • Low water flow
  • Dirty filter
  • High Phosphates
  • Time to shock chlorinate

Our technician visited a green pool last year that had five times the normal chlorine level and was still green! Why?  The pH of the water was so high that the chlorine was prevented from working and so it was not able to clear the pool.”

High pH

If the pH of your pool water is high, the effectiveness (or killing power) of pool chlorine is greatly reduced. This may cause the water to appear cloudy.  The orange line on the graph shows that when the pH is at 6.5, chlorine is 91% effective. It also shows that when the pH is 8.5, chlorine is only 9% effective.  In short, high pH “locks up” chlorine so check the pH regularly!

kill rate of chlorine

Low Water flow

It is vital that the pump you use is the correct size for your swimming pool. If it’s too small, then there will be insufficient water flow to filter the water properly.  Too large, and the high flow through the filter can cause the fine sand to be blown through the pipework and into your pool. Also, cloudiness may be caused from inadequate filtering time each day, even if your pump is the correct size. This means that there isn’t enough pumping time for all the water in the pool to be properly filtered and chlorinated.

High Phosphates

Sometimes, cloudy water has little to do with the size or cleanliness of your pool equipment or filter.  Bird and duck droppings, leaves, pollen and excessive dirt can also play a role in increasing phosphates which can lead to cloudy water.  A good information article about the facts and myths surrounding phosphates can be found here.

There are three solutions for murky water problems in this category.

  • First, a clarifier will gather the water borne particles into larger sizes that can be filtered out.  This process clears the water without any further action.
  • If the water is very dirty so that you can’t see the bottom, try using a flocculent to clear the murky water.  This will gather, or ‘flock’, the dirt in the water and bring them to the bottom of the pool where they can be then easily removed.
  • A skimmer basket sock helps filter finer particles which can also help reduce the amount of debris entering the filter. Using a sock will mean your filter stays cleaner for longer

High Calcium Levels

High calcium hardness levels can lead to cloudy pool water.  To check your calcium levels, take a water sample to your local pool shop.  They can test your calcium hardness levels for you. According to Australian Standards (1926.3), concrete pools require a calcium hardness level between 100-300 ppm. For fibreglass pools please contact your pool manufacturer to obtain the recommended levels for your pool.

Backwashing Dirty Filter

Most sand filters should be backwashed every 2 weeks during winter and every week during summer.  Cartridge filters should be cleaned at the same time intervals.  However, backwashing more frequently than this can lead to excessive sand loss, cloudy water and poor filtration.  Changing the sand in your filter every 7 years can be a great idea.  Old sand filters with the original sand inside will often have huge lumps of solidified sand that has bonded together inside the filter.  This means that the water is simply bypassing the sand and re-entering the pool.

Shock Chlorination – does your pool turn green several times a year?  Here’s why.

Regular shocking will remove the ‘dead’ chlorine (chloramines) from your pool and kill off most algae growth.  These chloramines ‘bind up’ the free chlorine and significantly reduce its effectiveness. Because of this, your pool water can have plenty of chlorine but still be green and stay green.  To shock chlorinate properly, most pools typically need at least 20 litres of chlorine. This should be done every 6 months.  Your pool shop can help you determine the right amount of chlorine needed to properly shock your pool.  Shocking at the beginning and the end of the swimming season is a great idea.

Final thoughts

Cloudy water is common during late Spring when the weather and water starts to warm up.  If the chlorination system remains on winter mode, then this can lead to low chlorine levels in the warming pool water which causes cloudiness.  As a rule, most pool pumps and chlorinators need to run for 4 hours a day in winter and 8 hours a day in summer to keep the water clear and safe.

References / Credits

dirty sand filter
Old sand filters with the original sand inside which has since partially solidifed
green pool
Pool water can have plenty of chlorine but still be green
PH Scale

Poor pH balance causes nearly every type of stain that our technical team see each day. Our photo gallery shows some extreme cases where the pH has been left to drift a long way above the suggested level. This pH increase causes stain producing minerals, metals, copper, calcium or manganese to bond to the surface of the pool interior leaving an unsightly stain that will not brush away. Thankfully, these stain issues can be rectified through our stain treatment process

We often tell our customers that if everyone kept their pool water balanced they would love their pool again and spend a lot less at the pool shop.

Try taking a water sample to your pool shop that is already pH balanced.  You’ll find that you save a lot of money on chemicals because the ‘foundation’ of your water chemistry is balanced. You may often find that you don’t need to buy any chemicals!

If your pH is too low, it means that your water is aggressive (or acidic) and that it will want to dissolve any materials that it can to try and rebalance itself.  This may include, the cement in your pool interior, tile grouting and even the copper piping in your solar or heat pump.

On the other hand, water that is very high in pH will try to re-balance itself by depositing (or precipitating) calcium, metals and minerals onto the surface of the pool or pipework. The result is a rough pool surface, calcium spots, mineral staining and sore eyes for swimmers.  Contrary to what many people think, incorrect pH is the main reason swimmers complain of sore eyes.  In most cases, chlorine levels have nothing to do with red eyes after swimming.

Remember that the pH scale is logarithmic so that it’s simple to use.  This means that small changes in the numbers are actually HUGE changes in practice.  For example, lemon juice has a pH of 2 and we can drink it without a problem.  However, hydrochloric acid is just a little lower on the scale at 0 but drinking this could be fatal.  This is because hydrochloric acid is actually 100 times more acidic than lemon juice.  Such a massive change in acidity just 2 digits down the scale!

Maintaining the correct pH level (7.4) in your swimming pool is one of the most important components of water chemistry.  If every pool owner did this regularly, we would go out of business!  This is because very few people would ever have staining in their pool.

Put simply water is either dissolving minerals or dumping them on the pool surface.  The only way to avoid this is to keep the water pH balanced

We suggest using a simple water testing kit to measure your pH each week.  It takes less than 15 seconds to do and may mean that you don’t have to visit the pool shop as often.  Many of our customers have been very grateful for giving them this advice. The reagents in these kits are used in some of the most sophisticated testing equipment used in pool shops today. When tested properly, the results from this test kit are very accurate.  Maintaining the correct pH is one of the best things you can do to keep your pool water clear.  Best of all, it may also save you a heap of money on pool chemicals at the pool shop.

water PH test kit