Why do I have to keep adding chemicals to my pool?

In a pool or spa, we need to help all the elements in your pool water achieve a natural balance whilst still making an effective and safe swimming environment.

Like everything in nature, water will always strive to be in balance

If your pool water is correctly balanced, this means that the waters chemical demands have been met. However, if chemical levels are out of the ideal ranges, the pool water can affect other areas of your pool. For example, it could seek the missing elements it needs by attacking the pool's surface and equipment or depositing additional elements onto the surface and equipment. This can lead to more expensive problems later if not corrected.

Also, if not properly balanced, the pools sanitising process (killing bacteria and algae) can be impaired.

The main 'variables' that affect the sanitising process are (click to skip to section):


The pH reading tells us whether the water is acidic or alkaline and incorrect levels may cause itchy skin and red eyes. The pH level ranges from 0 to 14, with 7.0 being neutral. Values below 7.0 are acidic. However, what is commonly overlooked is the understanding that pH is probably the most important factor to be considered when balancing swimming pool water.

The Australian Standard for pool water is between the range 7.0 to 7.8 with Rode Pools recommending 7.2 to 7.6 for in-ground concrete pools, 7.0 to 7.2 for fibreglass pools and 7.6 to 7.8 for spas. The pH level can change after heavy rain, heavy pool usage, topping up the pool, or adding chemicals, which in turn affects sanitising and therefore should be checked and adjusted frequently.

The effect of pH variation is most noticeable on the effectiveness of your chlorine to sanitise your pool. A typical domestic pool will aim for a chlorine level of about 1-2ppm.


TECHNICAL: Free chlorine is a measure of both Hypochlorous Acid (HOCL) and Hypochlorite ions (OCL-). The Hypochlorous Acid is the active part of the free chlorine which does the oxidising and destruction of contaminants. The Hypochlorite ion is inactive and can be considered the “reserve” that converts to Hypochlorous Acid as required.


When your pool has a pH of 7, the free chlorine has 75% Hypochlorous Acid (active) ions. If your pool has a pH of 7.8, the free chlorine has just 28% Hypochlorous acid (active) ions, making your sanitiser much less effective.

Therefore a swimming pool with a pH of 7 and a free chlorine level of just 0.5ppm has the same sanitising effect as a pool with a pH of 7.8 and a free chlorine level of 1.35ppm.

This is why the pH of your pool is really important.

T.A - Total Alkalinity

This is a measure of bi-carbonates, carbonates and hydroxides in the pool. We usually suggest 80ppm to 100ppm in swimming pools and 100ppm to 120ppm in spas is the accepted range, depending on the other balance factors. We can help you find the recommended level for your pool.

Low Total Alkalinity will lead to erosion of pool surfaces and corrosion of equipment. It will also cause the pH levels to be very unstable so small additions of other chemicals can result in major shifts in pH which is sometimes known as “pH bounce”. A low Total Alkalinity can also cause mild skin irritation and itchiness.

Adding Buffer (bi-carb soda) will RAISE the Total Alkalinity. Hydrochloric acid will LOWER the Total Alkalinity and the pH so these two chemical components need to be adjusted together.


TECH TIP: Hydrochloric acid must always be diluted (one part acid into ten parts of water) before being added to the pool and always add acid to water, never water to acid to avoid splashing onto yourself, others or surrounds.


When topping up the pool, depending on the on the Total Alkalinity of the top-up water and the amount topping up, this will affect the Total Alkalinity of the pool water.

Calcium Hardness

This is a measure of the amount of dissolved calcium in your pool water. Depending on your pool surface, we recommend a range between 250ppm and 350ppm for a typical concrete, marbelite or pebble pool. Calcium Hardness cannot usually be tested with the standard test kit so you will need to take a water sample to your nearest Rode Pools store for testing.

In most pools where calcium levels are not naturally high, you really only need to test a few times each year unless you are using Calcium Hypochlorite to sanitise your pool. This chemical raises Calcium Hardness levels, so more frequent testing and balancing may be necessary.


TECH TIP: When adding chemicals we suggest to increase in small amounts, run the filter and test the effect after several hours to avoid overdosing or encountering other problems.


If the correct balance of Calcium Hardness are not maintained, just like with Total Alkalinity, low levels cause corrosion to the pool surfaces and equipment and high levels will lead to scale formation.

Cyanuric Acid - Stabiliser

Cyanuric acid or as its more commonly known as ‘pool sunscreen' is used as a chlorine stabiliser in swimming pools to reduce chlorine loss due to UV rays (sunlight) if there is no pool cover. It should be added to the pool and maintained at approx. 50-70ppm. It binds itself to free chlorine and then releases it slowly to minimise degradation by UV light, extending the time needed to deplete each dose of sanitiser.

If the levels become too low, the effectiveness of your sanitation will be reduced because the free chlorine is being broken down by the UV light, which leads to the potential increase of algae growth.

On the flip side, if you regularly use powdered stabilized chlorine to sanitise your pool, your stabiliser levels can get too high and this can effectively block your sanitiser from being effective.


TECHNICAL: The higher the level of Cyanuric acid the more it reduce the effectiveness of free chlorine. To offset the loss of sanitisation power of free chlorine in stabilised outdoor pools the minimum concentration of free chlorine must be kept between 2ppm and 3ppm (ppm= parts per million).


Interestingly, Cyanuric Acid is not consumed or lost from swimming pool water unless due to splashing, backwashing or introduction of freshwater, these are the only times that you’ll need to add more Cyanuric acid.

For more information about your pool water balance, speak to one of our knowledgeable staff at your nearest store, call on 1300 007 665 or ask us a question on our Facebook page.