Whether you’re preparing your pool for the off-season or simply covering it to maintain cleanliness, knowing what to put under your pool cover is essential for protecting your investment and extending the lifespan of your pool equipment and structure. A quality pool cover acts as the first line of defense against debris, leaves, algae, and adverse weather—but it can’t do the job alone. What lies beneath the cover matters just as much as the cover itself.
In this article, we’ll take an in-depth look at the best practices for preparing and what materials to use under your pool cover, tailored for both in-ground and above-ground pools. We’ll also explore the science behind pool winterization and long-term maintenance, giving you expert-backed guidance that ensures your pool stays in excellent condition year after year.
Understanding the Purpose of a Pool Cover
Before we delve into what should go under a pool cover, it’s important to understand the roles a cover serves:
- Protection from debris – Leaves, dirt, insects, and twigs can muck up your pool water.
- Minimizing evaporation – Saves water and chemicals that might otherwise evaporate.
- Reduction of maintenance costs – A cover significantly reduces cleaning and chemical demands.
- Preventing algae growth – Blocking sunlight slows down or stops algae bloom.
- Seasonal winterization – Especially in cold climates, covers protect the pool structure during freezing months.
While a cover helps with all of these, what goes underneath makes all the difference in ensuring these benefits are fully realized. So let’s explore what you should put under your pool cover and why each item is essential.
Key Materials to Place Under a Pool Cover
1. Pool Cover Support or Safety Net (for In-Ground Pools)
For in-ground pools, the primary concern with winter covers is water accumulation. If too much rainwater or snowmelt collects on a tarp-style cover, it may sag and put pressure on the pool walls or even fall into the water.
A support system or safety net is typically used to prevent this. These are steel or aluminum rods anchored over the pool to create a concave or sloped cover surface that allows water to drain to the edges. Though technically not “goes under” in the literal sense, installing these supports before covering the pool helps maintain the integrity of the cover and the underlying components.
2. Safety Cover or Winter Cover
Before placing any materials under the cover, you need to ensure you’re using the right kind of pool cover:
- Winter covers – Designed to be durable and waterproof, they stay on for months and must resist freezing temperatures.
- Safety covers – Usually a mesh cover that allows water to drain but keeps people, pets, and large items from falling into the pool.
For in-ground pools, a solid winter cover is recommended for optimal protection. Place this directly over the pool once you’ve prepared the other under-materials.
3. Pool Cover Pump
This device goes on top and often under the cover. As snow and rain accumulate over your covered pool, water collects on the top or underneath the cover itself. In many cases, especially with solid covers, water can become trapped between the cover and the waterline.
A pool cover pump is placed on the surface of the cover (or may float between the cover and water) to remove surface water automatically. It’s crucial to ensure this is working during cold months to avoid structural stress and possible damage.
4. Pool Antifreeze (Winterization for Pipes and Equipment)
This one isn’t placed under the cover per se, but it’s a critical part of winterizing the pool and should be executed before the cover is placed. Pool antifreeze, commonly non-toxic propylene glycol, is poured into the plumbing lines to protect them from freezing.
This is done after:
- Draining the water below the return jets (or to levels dictated by pump and filter)
- Adding the antifreeze
- Capping the plumbing lines to prevent backflow
If not done, water left in pipes may freeze and cause cracks, leading to expensive replacements in spring.
5. Pool Chemicals: Winterizing Algaecide and Shock
Prior to placing the cover, you must balance the pool water chemically and sanitize it for the off-season. This involves:
Step 1: Balancing Water Chemistry
Correcting levels of:
- pH (7.2–7.6)
- Alkalinity (80–120 ppm)
- Calcium hardness (200–400 ppm for vinyl pools, slightly higher for concrete pools)
Step 2: Adding Winter Algaecide
A commercial-grade winter algaecide is designed to keep your pool free of algae for months and should be applied at or near the manufacturer’s recommended dosage.
Step 3: Shock Treatment
A heavy dose of chlorine or non-chlorine shock is added to kill off any existing bacteria or contaminants before placing the pool cover.
Finally, it’s wise to use stabilized chlorine tablets in a floating dispenser or place them in the skimmer basket if the system allows. This provides continuous sanitization under the cover.
6. Pool Pillows (or Airbags for In-Ground Pools)
A somewhat unexpected yet critical step is placing winterizing airbags or floating pillows under the cover across the deepest part of the pool.
As water freezes, it expands. Without these air pillows, that expansion can press against the pool walls and cause damage—especially to vinyl or fiberglass linings.
These airbags create a void or buffer that allows the ice to expand upward, reducing pressure on the pool structure. They are usually chained in place or tethered to avoid floating and should never be used with safety net covers but only with solid winter covers.
How to Prepare Your Pool for Winterization
To ensure that the materials placed under your cover do their job, follow this general step-by-step guide to prepare your pool for a long period under cover:
- Thoroughly clean your pool – Brush walls, vacuum debris, and clean filters.
- Test and balance water chemistry – Use a digital or liquid test kit to ensure levels are correct before adding winterizing products.
- Shock the pool – Add a strong dose of chlorine or non-chlorine shock.
- Add winter algaecide – Follow label directions or consult professionals for guidance depending on your pool type.
- Drain the water appropriately – Typically, it should be lowered 6–18 inches below the skimmer, depending on equipment and climate.
- Winterize equipment – This includes pumps and filters; some will require drainage, while others may use antifreeze.
- Insert air pillows – If you have an in-ground pool, place them carefully and securely in the deepest areas.
- Secure your pool cover – Use water bags, anchors, or a combination to ensure it stays in place through the off-season.
Each of these steps impacts the efficiency and safety of what lies beneath your pool cover. Skipping even one can have a detrimental effect when you uncover the pool in spring.
Material-Specific Guidance for Pool Covers
Different pool types (in-ground vs. above-ground) and different cover types (solid, mesh, safety, solar) will alter what you’re supposed to place underneath (or above) your cover. Here’s a breakdown tailored for specific scenarios.
For In-Ground Pools Using Solid Winter Covers
Solid covers provide maximum protection but are the most susceptible to water buildup. Because of this, you must use:
- A waterproof winter cover rated for your climate
- Winter cover supports to hold up the cover weight or slope it
- Pool cover pump on top and accessible for maintenance
- Air pillows suspended in the deepest section to buffer ice expansion
- Proper chemical treatment, including stabilized chlorine, algaecide, and balanced water
The placement of each of these under (or on) the cover significantly impacts the success of your seasonal cover system.
For Above-Ground Pools
Above-ground pool owners generally do not use air pillows or support structures since the water level can be left the same under the cover. However, the steps for chemical treatment and cover security remain largely the same:
- Balance water chemistry and shock it
- Use a mesh or solid cover with a cover pump for regions with heavy rain or snowfall
- Leave water at a level 4–5 inches below the skimmer
- Store pool equipment indoors if freezing temperatures are expected
Some above-ground pool covers come with built-in straps and tension mechanisms, making anchor kits unnecessary. Still, ensure nothing shifts or allows contamination through gaps.
For Solar Covers (Seasonal Use, Not Winterization)
Solar covers are distinct in both purpose and usage and will typically be used to retain temperature in an active pool. However, when used during short-term shut-downs or in temperate climates:
- Balance water and shock the pool before placing the cover
- Place the solar cover with the bubble side down to trap heat and retain energy
- No air pillows or support structures are necessary
Solar covers do not provide complete protection from leaves but reduce evaporation and heat loss significantly better than typical mesh or tarps.
The Role of Water Level Under a Pool Cover
The water level under your pool cover is often overlooked but critical in determining maintenance levels and pool health during downtime.
Water Level: In-Ground Pools
For winterizing:
- Lower water to about 6–18 inches below the skimmer intake
- This level helps you avoid frozen water in the skimmers and pump systems
- If using air pillows, ensure the water level supports maximum expansion
Too much water under the cover poses a risk to the cover itself, while too little risks the structure from damage due to frost heave in certain soil types.
Water Level: Above-Ground Pools
Above-ground pools often require that water remain at skimmer level so the cover can maintain tension and the walls remain upright:
- Do not drain below 4–6 inches of skimmer mouth
- This helps maintain the pool’s structural integrity while covered
- Draining it completely can warp the walls or lead the pool to collapse in strong winds
Potential Mistakes to Avoid
To keep your pool in great shape under a cover, here are a few common missteps that can have long-term repercussions:
- Skipping the final water test – An improperly balanced pool invites algae and staining even under a cover.
- Using improper chemicals – Only use algaecides labeled for winter protection. Regular varieties may not last.
- Not using or misplacing air pillows – For in-ground pools, failing to install or incorrectly placing air pillows can lead to expensive structural damage.
- Securing the cover poorly – Whether with improper anchors or loose straps, a shifting cover can expose parts of the water to debris and sunlight.
- Using a summer cover for winter – Summer covers, like solar blankets, are not meant to protect against snow, rain, or long-term elemental exposure.
Choosing the Right Pool Cover for Optimal Performance
The key to proper under-cover maintenance is starting with the right cover. Here’s how they compare based on your needs:
| Cover Type | Best For | Pros | Cons |
|---|---|---|---|
| Solid Winter Cover | Full off-season protection in freezing climates | Superior protection, blocks sunlight, supports air pillow & hardware | Potential for water accumulation; requires maintenance |
| Mesh Safety Cover | Year-round safety and light debris reduction | Allows water to drain, extremely durable, good for children and pets | Let’s sunlight in; can still get some algae without algaecide |
| Solar Cover | Swimming seasons, energy retention | Efficient at heating and evaporation reduction | Not suitable for long-term shut-down or freezing weather |
Choosing the right type of cover can determine whether chemical support, water management, and equipment protection are sufficient under the cover to survive months of off-season wear.
Conclusion: Proper Pool Cover Preparation Protects More Than Just Water
Now that you know exactly what to put under your pool cover, it becomes clear that effective pool winterization is about far more than just placing a tarp over the water. It encompasses careful preparation, chemical treatment, equipment protection, and understanding physical properties like freezing and expansion that impact your investment.
By preparing your pool with balanced water chemistry, appropriate algaecide and shock, air pillows, and a secure cover system, you ensure the swim season begins trouble-free next year. Each component placed beneath or beside the cover plays a specific, vital role in keeping your pool clean, safe, and durable.
For any pool owner, especially those who face long winters, understanding and applying this checklist before placing a pool cover isn’t just a maintenance tip—it’s a financial and structural defense strategy.
Let your cover do its job properly—and don’t forget what needs to be in place before you put it on.
Expert Takeaway
If you’re ever unsure how to properly winterize your pool or what to place under your pool cover, it’s always wise to consult with a local pool service professional. Their expertise can help tailor steps to your specific climate, water chemistry, and pool structure, ensuring your cover serves its purpose efficiently for years to come.
What materials are recommended to place under a pool cover?
To protect your pool during the winter months, it’s important to use the right materials beneath your cover. A pool cover pad or a layer of foam padding is often recommended to prevent abrasion between the cover and the pool walls. These materials help reduce wear and tear caused by debris, ice, and fluctuating water levels. In addition, pool blankets or solar covers can also be used underneath to provide insulation and help maintain water temperature, which can be beneficial in extremely cold climates.
For inground pools, a safety cover should be the final layer, securely fastened to the deck for stability. If you have a mesh cover, water will drain through, so it’s important to ensure the area around your pool is graded to allow proper runoff. Solid covers require the use of a water bag system or a cover pump to remove standing water. By choosing the right materials and installing them properly, you can help ensure your pool remains clean and structurally sound throughout the winter.
Can I leave water in the pool when winterizing it?
Yes, you can leave water in your pool when winterizing, but it must be properly balanced and maintained. The water level should be lowered slightly below the skimmer to prevent damage from freezing temperatures. If the pool is completely drained, it can cause structural problems, especially in inground pools, due to hydrostatic pressure from the ground. However, maintaining the proper water level allows for the correct placement of winterizing chemicals and ensures that the pool cover is installed safely.
In addition to monitoring water levels, it’s crucial to thoroughly clean and balance the water before covering the pool. This includes adjusting pH levels, alkalinity, and calcium hardness. A winterizing chemical kit and algaecide should be used to keep the water clean and inhibit algae growth during the off-season. Covering the pool with a secure cover after these steps ensures the water remains stable and ready for opening in the spring.
Should I put anything over the pool cover besides water bags?
Water bags are commonly used to secure a pool cover and prevent debris from collecting, but there are additional steps you can take for winter protection. Cover reels or tie-down straps can be helpful for keeping the cover taut and reducing sagging. Leaf netting or a leaf rake system can also be installed to catch debris before it reaches the cover, making spring cleanup easier. In some cases, people use pool cover pumps to remove excess water that accumulates on top of solid covers.
However, adding too many items on top of the pool cover can cause unnecessary stress and damage over time. Heavy objects like patio furniture or large tarps should be avoided, as they may tear the cover or trap moisture underneath, leading to mold and mildew. The best approach is to use water bags or a cover pump and ensure your cover is securely fastened around the edges or deck anchors to maintain stability and protection throughout the winter.
Do I need to drain my pool before putting on the cover?
No, you should not completely drain your pool before putting on the cover. In fact, most experts recommend leaving the pool partially filled to protect the structure. For inground pools, draining the water below the level of the skimmer and return jets is standard. This protects the plumbing and skimmer from ice expansion damage. For aboveground pools, lowering the water level to about 4–6 inches below the top rail is ideal. Draining all the water increases the risk of the pool shifting, cracking, or collapsing under ground pressure.
Before partially draining your pool, it’s essential to winterize the plumbing by blowing out the lines and adding pool antifreeze as needed. Once the proper water level is achieved and chemicals are added, the pool cover should be placed securely over the remaining water. Completely draining the pool may be appropriate only in extreme cases, such as when preparing for repairs or long-term closure. But for standard winterization, always maintain some water to keep your pool in good condition through the cold months.
Is it necessary to vacuum the pool before covering it for winter?
Yes, it is highly recommended to vacuum the pool before covering it for the winter. Leaving debris such as leaves, dirt, and algae in the pool over the off-season can lead to staining, scaling, and increased chemical demand when you reopen. Vacuuming thoroughly will clear the floor and prevent settled particles from breaking down in the water. It’s also important to brush the walls and tile line to remove any clinging algae or organic matter that could cause problems in the future.
Ideally, vacuuming should happen after balancing the water and adding winterizing chemicals but before lowering the water level and installing the cover. This ensures that the debris removal is as effective as possible and that the water chemistry remains stable under the cover. If you are using a mesh cover, be aware that some fine particles may still get through over time, so a final pool vacuum after removal of the cover in spring will help ensure a smooth opening process.
How do I prepare the pool chemicals before covering it for winter?
Preparing your pool’s chemical balance before covering it for the winter is a critical step in protecting the water and pool surfaces throughout the off-season. Begin by testing the water for pH, alkalinity, calcium hardness, and chlorine levels. The ideal pH range is 7.2 to 7.6, total alkalinity should be between 80 and 120 ppm, and calcium hardness should be around 200 to 400 ppm for concrete pools or 150 to 250 ppm for vinyl pools. Adjust these values accordingly before proceeding to winterizing chemicals.
Once the balance is correct, add algaecide and a winterizing chemical kit, which often includes a stain and scale inhibitor and a chlorine booster. This combination helps preserve water clarity and prevents algae growth and metal staining during the winter. Allow the water to circulate for a few hours after adding chemicals to ensure even distribution before covering the pool. This careful chemical preparation can significantly reduce the time and effort required when reopening the pool in the spring.
Can I reuse the water in the pool after removing the winter cover?
In most cases, you can reuse the pool water after removing the winter cover, provided the water level was maintained properly and the pool was adequately winterized. If the pool was covered correctly and the water remained at the appropriate level, only some minor chemical adjustments should be needed. These adjustments usually include rebalancing the pH, alkalinity, and chlorine levels. However, if the cover leaked or let in a significant amount of debris and rainwater, partial draining and filtration may be necessary.
Spring pool maintenance also involves removing accumulated leaves and dirt using a leaf net or vacuum. If the water appears cloudy or has a strong odor, that could be a sign of algae growth or chemical imbalance and may require shock treatment. Cover pumps often help keep the winter cover dry, reducing water loss, but if the water level dropped too low over the winter, you may need to add fresh water before balancing and starting the filtration system. Overall, with proper winterization, your pool water can typically be reused without the need to drain and refill the entire pool.