Once the cover is on and the temperature drops, it’s easy to stop thinking about your pool. Out of sight, out of mind, right? Don’t get too cozy and comfy, though.
Even though your pool is technically “closed,” there’s still plenty happening under the surface, both in terms of water chemistry and how your pool responds to what was left behind at closing.
The good news? If you took the time to properly treat your water before closing, your pool is quietly benefiting from it all winter long.
Here’s a closer look at what’s going on beneath the cover and an explanation of how the steps you take in the fall can make all the difference come spring.
1. Water Chemistry Continues to Shift
Just because your pool isn’t being used doesn’t mean the chemistry is frozen in time. Even in cold water, chemical levels can slowly change due to rainwater seeping in, debris that made it under the cover, organic material that was left behind, and temperature swings that affect pH and hardness.
If your water wasn’t balanced before closing, these changes can start to cause:
- Scaling on surfaces or tile
- Corrosion in heaters or fittings
- Staining caused by metals or organic debris
- Algae growth if sanitizer levels weren’t stabilized
If you balanced everything before closing, you’re already ahead. But that balance only lasts if there’s something supporting it through the off-season.
2. Organic Waste Is Still Breaking Down
Even a clean-looking pool can hold residual waste from swimmers, leaves, pollen, or runoff. This waste doesn’t disappear just because the pool is closed; it slowly breaks down over time, creating the perfect environment for waterline scum, odors, springtime cloudiness, and elevated chlorine demand when you reopen.
What helps:
A final dose of ENZymePRO® before closing continues to break down these contaminants throughout the off-season. It works alongside your sanitizer (or residual sanitizer) to eliminate waste before it becomes a bigger issue in the spring.
3. Phosphates and Metals Don’t Just Sit Idle
Phosphates, which are often introduced through leaves, dirt, and plant debris, act as food for algae. And even if your pool water is cold enough to slow algae growth, phosphates will still be present when you open in spring, ready to feed any spores that survived the winter.
Likewise, metals like copper or iron can settle and cause staining on pool walls and floors if they’re not removed before closing.
What helps:
Revive!® START UP/CLEAN UP is designed to handle both of these problems. If you used it as part of your closing routine, it’s currently:
- Removing up to 2.0 ppm of metals
- Eliminating up to 2000 ppb of phosphates
- Binding and settling out fine debris
- Helping prevent staining and discoloration
And it’s doing it all without interfering with other closing chemicals.
4. Stuff Is Still Entering the Water
Even with a well-fitted safety cover or tarp, small amounts of water, debris, and sunlight can find their way into the pool.
As those elements mix with your existing water, the risk of algae, scale, or contamination increases, especially if the water wasn’t clean and balanced before the cover went on.
That’s why closing a clean pool with proactive treatment is so important. You’re not just protecting it for the winter; you’re also setting it up for an easier, cleaner opening in spring.
5. Your Pool Is Either Getting Better or Getting Worse
In the off season, your pool is sitting still. There’s no filtration, no brushing, no swimmer circulation. That means what’s in the water now is what you will be dealing with when you open your back up.
If your water was clear, balanced, and treated, it’s likely to stay that way.
If your water was cloudy or unbalanced, that damage continues silently all winter.
It’s not too late to make a difference. If you’ve already closed but didn’t add phosphate remover or enzymes, you can still lift a corner of the cover and apply a final treatment of enzymes. We wouldn’t recommend adding phosphate remover if the pool is closed and can’t be fully cleaned.
Final Thoughts on What's Happening Under Your Pool Cover
What’s happening under your pool cover right now? That depends entirely on how you closed.
The right steps at closing—and the right support products between seasons—can actively protect your water and surfaces all winter long, even when the pool is out of sight. So when opening day rolls around, you’re not starting from scratch. You’re starting from a clean, clear foundation.
It’s the work your pool is doing now that will save you time, money, and effort later.
