As the last traces of winter fade and temperatures begin to rise, pool owners prepare to bring their pools back to life. But before you remove that cover and dive into the reopening process, have you ever wondered what happens to your pool water during winter?
The chemistry of your pool undergoes significant changes during the colder months. Without proper maintenance, winter can leave behind cloudy water, stubborn algae growth, imbalanced chemistry, and even damage to your pool’s surfaces and equipment. Understanding the science behind these changes can help you avoid surprises and ensure a smoother, stress-free spring opening.

What Happens to Your Pool Water During Winter?

1. pH Levels and Alkalinity Shift

Cold temperatures slow down chemical reactions, but that doesn’t mean your water chemistry stays stable. Over the winter months, pH and total alkalinity levels can fluctuate due to environmental factors like precipitation, organic debris, and lack of circulation. A drop in pH can make your water more acidic, potentially leading to corrosion of pool surfaces and equipment, while high alkalinity can cause scale buildup.

2. Algae and Bacteria Growth

One of the biggest misconceptions about winter is that algae and bacteria stop growing. While cold temperatures slow their development, they don’t eliminate them—especially if your pool wasn’t properly treated before closing. Algae spores can survive in covered pools, and as soon as temperatures rise, they multiply quickly, turning your water green or cloudy.

3. Chlorine Loss and Contamination

If you didn’t add a winterizing algaecide or maintain a chlorine residual, your sanitizer levels likely dropped over the season. Chlorine naturally degrades over time, and without circulation, it becomes ineffective at killing bacteria and preventing contaminants. This leaves your pool water vulnerable to organic matter like leaves, dirt, and pollen, which contribute to cloudy or discolored water.

4. Calcium Hardness and Scale Formation

Calcium hardness levels play a crucial role in preventing pool surface damage. When water sits stagnant for months, calcium can either drop too low (leading to corrosive water) or rise too high (causing scale formation on pool walls and equipment). Properly balancing your calcium hardness in spring helps protect your pool finish and equipment.

5. Debris and Organic Matter Accumulation

Even with a pool cover, fine debris, pollen, and rainwater can find their way into your pool. If left untreated, organic matter starts breaking down, leading to increased phosphate levels—a primary food source for algae. That’s why pools often open with murky water or a strong odor if they weren’t properly prepped in the fall.

How to Reverse Winter’s Impact for a Smooth Pool Opening

Now that you understand what happens to your pool water over winter, here’s how to restore balance and clarity for a smooth opening:

✔️ Test & Balance the Water – Start by checking pH, alkalinity, calcium hardness, and sanitizer levels. Adjust them accordingly to restore proper balance.

✔️ Shock the Pool – A high-dose chlorine shock helps eliminate bacteria, algae spores, and contaminants that built up over the winter.

✔️ Brush & Vacuum – Scrub pool walls and floors to remove algae or biofilm buildup before restarting the filtration system.

✔️ Run Your Filtration System – Allow your filter to run continuously for at least 24-48 hours to help circulate and clear the water.

✔️ Use Algaecide & Clarifier – Adding preventative treatments ensures your water stays clear and free from algae regrowth.

Get Your Pool Ready with Expert Help

Spring pool opening is more than just removing the cover—it’s a science that requires the right chemical balance and proper steps to restore water quality. Whether you’re a homeowner or a commercial facility, our professional pool service team is here to ensure your pool is ready for a clean, safe, and enjoyable season.

📞 Contact us today to schedule your pool opening service and let us take care of the hard work for you!