Rain water – How does it affect my swimming pool?

rain in ground swimming pool storm filterdeal


Rain is a good thing, right? Farmers need it for their crops and it keeps our lawns and landscaping lush. But when it comes to your pool chemistry, it can be a cause for headaches.


Rain water is known for it’s acidic properties, which can spell trouble after a large storm or downpour. Although light rain shouldn't cause much harm, testing your water after every shower is a good practice to adopt as proper chemistry should always be maintained.


Ideally, swimming pool water should have a pH of 7.4. The reason for this is that the human eye and mucous membranes have a natural pH of 7.5. Keeping to a relatively similar pH level aids in keeping eye irritation at bay for you and your pool guests. Conversely, rain water typically has a pH of around 5.0. As this mixes with your pool water, it will alter pH levels. When the pH levels creep away from 7.4-7.5, this is grounds for annoying eye irritation and other problems. For example, it is common for eye redness or irritation to be blamed on high chlorine levels, but often times it can be a result of water pH that is too low.


Additionally, runoff is a serious problem for in-ground pools in particular. Along with altering pH levels, it is the quickest way for dirt and other debris to end up in your water, as well as raising water levels well above normal in any type of pool. Calcium hardness, alkalinity and free chlorine levels could be all over the place following a good soaking.


Hail stones swimming pool filterdeal
Hopefully this isn't a site you ever see in your backyard!


So Mother Nature just let loose… Now what?

The storm of the century (or probably just this week) came and went. Water levels could be well above normal, diluting the balanced chemistry you work hard to maintain. Leaves, dirt, and other unwanted debris are soiling your otherwise crystal clear backyard oasis, possibly increasing nitrogen and phosphorus levels which can promote algae and bacteria growth.


skimming swimming pool leaves after storm


Your first line of defense is to skim off any unwanted floating visitors, followed by a good sweeping to remove what’s below the surface.


Next you will need to drain any extra water. If you have a D.E Grid system, put the multi-port valve from vacuum to waste mode. This will eliminate extra water without putting it through the filter. Make sure to turn off the pump beforehand and attach a waste line or backwash hose. Turn the pump back on until the water drains to normal levels. Shut the pump off, turn the valve to the filter position and turn the pump on again.


For cartridge filter systems, the draining process is different as these systems are not designed for reverse water flow through the filter system. Start by turning off skimmer flow so suction comes from the main drain, preventing the influx of air as the water level lowers. Attach a hose, then open the bypass valve so water does not flow through the filtering system. Turn system on, making sure to closely monitor the water level inside the pool. If you have a variable speed pump, using the high speed mode will accelerate this process.


With both types of systems, always be careful not to drain the water below the skimmer. If you do happen to drain too much, adding water to your pool can also alter chemistry. A smart step to take in preventing fluctuations in chemistry when topping your pool off is to use a garden hose pre-filter, like the Max Clear™ Ion Exchange Pre-Filter. Pre-filtering removes common minerals including calcium, magnesium, iron, lead and copper as well as lime scale, chemical contaminants, algae, mold spores, bacteria, and organic debris.


Once water levels are back to normal, you are in a good position to address your water’s chemistry. Run water through your typical testing process, keeping an eye on pH and alkalinity levels. Low pH levels can cause eye irritation, damage to liners, and can sometimes even damage mechanical components of your pool, while levels that are too high can lead to poor chlorine disinfection, skin irritation, and cloudiness.


cloudy swimming pool dirty water bad ph filterdeal

If your pool water seems cloudy, high pH could be the culprit.

There are many recipes and chemical combinations to maintain the chemistry of your water- if you are unsure of what is needed specifically, it’s never a bad idea to take a water sample to your local pool & spa store. After an assessment, they can easily recommend specific chemicals based off of your particular routine to return your pool to the backyard oasis that it is!



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