How Rain Affects your Pool

In times of heavy rain, how is your pool water affected and more importantly, what you can do about it? 


The rain can definitely have an adverse effect on you swimming pool water, though it may come as a surprise that the problems caused by rain are not a result of 'dilution' of the chemicals in your pool. An inch of rainwater added to a typical 50,000 litre pool increases the amount of water by only about 1.5%, meaning dilution is not usually an issue.
It's more about what comes into the pool with the rain. Rain delivers algae spores, which are usually present in the air airborne debris to pool water and it is these things that cause problems. When it rains, these spores and other material in the air above a swimming pool get washed into the water. 
All of this material reacts with your pool chlorine and so reduces the active chlorine level in the water. Combined with this, when the organic matter decomposes it provides fuel (phosphates) for the growth and reproduction of algae and other simple organisms in the water. Combined with sunlight, especially in warmer water, the conditions become perfect for accelerated growth of algae in the pool.
When you have rainwater coming off your landscape or deck, you also have an added source of water and debris to deal with. When rainwater and ‘run off’ enter the pool, they can change your water’s pH, calcium hardness, total dissolved solids (TDS), alkalinity and other chemical levels as well as bring contaminants (e.g. debris, dirt) into the pool.


So, what to do? 

The extra debris added to the pool with rainfall can affect the pool water chemistry. For this reason, it is important that you test your water after it rains and re-balance if necessary. If the Total Alkalinity of your pool water is within the ideal range, then the pH of the rainwater will not significantly affect your pool water balance.


The solution is to make sure that the rate at which the algae in your pool are being killed is faster than the rate at which they are reproducing. This means raising the sanitiser (chlorine) level up, much higher than the ideal range, balancing the pH level, adding an appropriate algaecide, clarifier and oxidiser. By adding these chemicals and running the filtration system for a minimum of 24 hours, this should return the pool to crystal clear again.


After the rain has subsided, you will need to drain the excess water from the pool, allowing for proper skimming of the pool surface.  If your filter has a multiport valve, you can simply set the filter valve from filter onto waste, lowering the water level.


With very heavy rains, runoff from gardens and surrounding areas of the pool can add large amounts of dirt, garden soil and even mud into a pool. This will turn the pool into a messy brown soup with the inability to filter out. This is where a floccing agent is used to bind the suspended particles together and drop them to the floor of the pool to make it easier to remove by vacuuming directly to waste.


If you require help with any of these techniques please come into our one of our stores and speak with our experienced team or book your service online below.