Last Updated on October 18, 2021
“Why is my pool green after it rains?“, this is the question new pool owners usually ask after heavy rains have come down on their property. Well, the answer to that question can be all be attributed to your pool’s water chemistry.
Why Your Pool Is Green And Cloudy
Rain introduces a lot of new things to your swimming pool from dirt, debris, and of course, fresh unchlorinated water. These affect your swimming pool by diluting the existing balanced water chemistry that allowed you to have clean and pristine water before it rained.
How much does rain dilute your pool?
Let’s use a 20 feet by 40 feet pool that has about 500 gallons per inch of water as an example here. If the recent rain was able to add 2 inches to your pool’s water level, then that’s 1,000 gallons of rainwater.
That might not be that much, but you also have to consider that this unchlorinated water may also contain contaminants like debris, dirt, and other organic elements. This in turn reduces the free chlorine levels in your swimming pool and adds to the organic debris loads in your pool water.
Once free chlorine levels start to go down and ultimately reach zero levels, algae growth begins and will continue to grow until you work on a solution to fix the green water in your swimming pool.
How To Fix A Green Pool After Rain
Once the rain has stopped and you’ve seen your pool water become green, a thorough cleanup is necessary before you can start using your swimming pool again. The following guide will help you fix your pool after a rainstorm.
Remove large debris from the water
It’s typical for large debris to go into your pool after heavy rains, especially if it’s left uncovered. Since debris can influence the chemistry of your pool water, and even stain your pool walls and floor, it’s best to remove them as soon as the rain stops.
Empty pool skimmer and pump baskets
The accumulated debris can clog the baskets and skimmer, and these will reduce the water flow rate, so make sure you empty both the pool skimmer and pump baskets before you run your pool pump.
Adjust pool’s water level
Rain can add inches of water to your pool. Some pools may overflow because of this and some can automatically drain excess water. Depending on the type of pool you have and the system you’re using, you can open the water drain, backwash your filter if you’re using a sand filter, or simply follow the instructions for your pool system to get the water level back down to around the center of your skimmer float.
Test pool’s water chemistry
- Includes .75 oz reagent bottles
- High Range (HR) kit
As we’ve mentioned before, rainwater can dilute your balanced pool water. The best way to fix a pool with green water is to test your water chemistry first and see what kind of adjustments you have to make to balance it.
In normal circumstances, your pool should fall within the following ranges, but you still have to check your manual for specific instructions about your current pool setup:
- pH: 7.2 – 7.6 A lower pH level can cause skin and eye irritation. A higher pH level can cause calcium scaling.
- Total Alkalinity: 100-150 ppm. This helps prevent spiking of your pH levels. Commonly referred to as the shock absorber.
- Calcium Hardness: 200 to 400 ppm. Must maintain proper level to prevent water from being too corrosive or end up with a calcium/scale buildup problem.
Run the pump and filter the water
Make sure that the water in your pool can circulate properly. Once you’ve determined that it does, then you must let it run for some time and see if the green water will disappear. The amount of time needed to run your pool equipment may vary depending on your pool setup. Sand filter systems may need several days, while diatomaceous earth or DE filters only need a few hours.
Give the pool a shock
- Powerful chlorine shock treatment that is great for regular maintenance.
- Quickly eliminates algae, bacteria, and other harmful contaminants from your pool water.
- Main active ingredient is 68% Calcium Hypochlorite (Cal-Hypo) for quick sanitizing.
- Dosage: 1 Pound per 10,000 gallons
If for some reason your pool water is still green after the rain, then you must prepare to shock your pool. Maintaining a higher shock level will help kill and remove all the algae in your pool but this may take multiple treatments before it’s safe for you to use your pool again.
You need to double-check if your filter system is working properly and your water chemistry is at the proper levels. Also, it’s best to shock your pool in the evening or early morning. You need to mix your pool shock treatment and slowly pour this mixture into your swimming pool.
Warning: Do NOT add the pool shock directly to your skimmer.
While you’re shocking your pool, try to brush and clean the pool daily to remove the dead algae and other debris on your pool surface.
Test pool water again
Once your pool is back to its usual color, you should test your water chemistry levels again. If it’s on the proper levels, then you can go ahead and use your swimming pool again. If not, then make the necessary adjustments and give it some time before you start using your pool.
What You Can Do To Avoid Green Pool Water
If you’re not fond of fixing green pools caused by rainstorms, then you should consider doing these steps to prevent dilution before it even occurs.
Check Weather Forecasts
It’ll be difficult to prevent rain from entering your pool when it’s already raining outside. The best way to remedy this situation is by simply checking the daily weather forecast and securing your swimming pool when there’s a good chance that rain will be hitting your area soon.
Cover Your Pool
Before it rains, it’s recommended that you pull the cover in place to avoid rainwater mixing into your balanced pool water. Getting a good quality pool cover can be a great investment since low-quality pool covers are thin and can easily deteriorate which may allow rain to enter your pool.
- BENEFITS: Kills and prevents all algae types including green, black and mustard algae in your swimming pool so you can enjoy your summertime fun
- USE: Apply directly to the pool for easy DIY pool care
- COMPATIBILITY: Great for vinyl-lined and saltwater pool systems
- FEATURES: Non-foaming algaecide formula destroys algae fast for crystal clear water; Swim 15 minutes after applying algaecide to your pool; Dissolves fast; Won’t fade vinyl pool liners
If covering your pool is not an option, you can still avoid getting your pool green by adding algaecide to the water. It’s also best to remove any debris already in your pool like leaves, branches, or twigs.