After a long (but not very wintery) winter, pool opening season is in full swing! This welcome time of year symbolizes a summer of fun is right around the corner. After months of staring at a winter cover on your pool seeing the pool water underneath is a sight for sore eyes.

But what many pool owners with safety covers are finding this spring, is a green pool staring back at them when that cover finally comes off.

If your pool water is green when you take off your safety cover, it is likely due to algae growth in the water. Algae are tiny plants that can grow in your pool when conditions are right, such as warm temperatures, sunlight, and the presence of nutrients in the water.


Safety covers are porous, so small amounts of dirt and debris filter through the cover during the off season. This dirt is the nutrients algae needs to feed on to grow. Combine that with a stunning October with temperatures well in the 20’s, you have the perfect environment for algae.

What to do

To address the green water in your pool we recommend:

Shocking the pool with a high dose of chlorine to kill the algae. Note, it takes up to 48 hours for shock to do it’s job. Brush the pool walls and floor to remove any algae clinging to the surfaces. If your using a sand filter, backwash after brushing, wait 24 hours, brush and backwash again. If you’re using a cartridge filter you’ll need to clean your cartridges after removing the algae from the pool. If you have a safety cover and a cartridge filter we do recommend having a spare set of cartridges for this type of situation. Old cartridges will always come in handy at least once – so hang on to the old ones when you replace them.

To ensure you’re good to go, bring your water in for testing before taking that first plunge.

If you have booked Pool Craft to open your pool we will get the ball rolling on algae clean-up. Our team will shock your pool and give your walls a scrub. If you’ve booked a vacuum we’ll handle that also, but in some cases you may want to book a return visit to clear up algae for an additional charge. We’re happy to help get you swimming, but it may take us a few days to schedule you’re return visit. This is the busiest time of year for us and we don’t want to let anyone down, so pre-booked services will take priority.

Preventative Measures

There is no perfect solution to prevent algae from forming under a safety cover. Our recommendation to minimize the chances of this happening – close your pool late in the season, and open it early. Worried about frost if you close later in the fall? If you have automation chances are you have freeze protection, so your system will automatically turn on when the temp drops on chilly fall nights, protecting your pipes and equipment that hasn’t been winterized yet.

Don’t let this put you off safety covers – they are so valuable in keeping your pool safe in the off-season! Just keep this in mind when your cover comes off. Allow up to two weeks for your water to be swim-ready post-opening.