How to Use a Solar Pool Cover

Reviewed by a Certified Pool Technician (CPT)

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The Short Answer

A solar pool cover works best when the bubble side faces the water and the smooth side faces up. Keep the cover on whenever the pool isn't in use to reduce evaporation, retain heat, and minimize chemical loss. Remove it before shocking the pool, and wait until free chlorine returns to 1–3 ppm before replacing it. Store the cover out of direct sunlight when not in use.

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A solar cover is one of the highest-return accessories available for pool owners. It extends the swim season, reduces heating costs, cuts chemical consumption, and keeps debris out all from a sheet of UV-resistant plastic that costs 50–200. The key is using it correctly. Most solar cover problems (algae, discoloration, premature wear) trace back to a few specific mistakes this guide addresses directly.

Step-by-Step Guide to Using a Solar Pool Cover

Step 1: Size and Trim the Cover

Purchase a solar cover larger than your pool's actual dimensions; you'll cut it to fit. Measure your pool's length and width (or diameter for round pools) and choose the next standard size up.

To mark the cut line: Lay the cover over the pool surface and use a felt-tip marker to trace the pool's edge from underneath. Remove the cover and cut along the marked line with sharp scissors or a utility knife. A slight ¼–½ inch gap from the pool wall is fine; you don't need a perfect seal, just good surface coverage.

Cutting doesn't void the warranty. Per manufacturer guidance for most major solar cover brands: cutting to size is expected and does not affect warranty coverage, which applies to seam separation and manufacturing defects, not bubble degradation or edge condition after cutting.

Step 2: Deploy with Bubbles Down

Place the cover on the water with the bubble side (textured side) facing down, touching the water. The smooth side faces up toward the sun.

The bubbles trap air pockets that act as insulating chambers between the cool pool water and the warm air. They also increase the surface area in contact with the water, improving heat transfer. Placing the cover bubble-side down is not optional, it's what makes solar covers function. (Bubble-side up actually reflects heat back rather than retaining it.)

Step 3: Cover the Pool Whenever It's Not in Use

The more hours the cover is on, the greater the benefit. Cover the pool:

• Every night (overnight heat loss without a cover is 4–7°F in most climates)

• During the day when the pool isn't being used

• During extended cloudy periods (cover still reduces evaporation and chemical loss)

• Before storms (keeps rain dilution and debris to a minimum)

Remove it for swimming; swimmers can't safely enter a covered pool, and the cover traps body heat and reduces circulation during use.

Step 4: Remove Before Shocking and Chemical Treatments

This is the most commonly skipped step and the source of most solar cover damage. See the chemistry section below for the specific rules.

Step 5: Roll Up and Store Properly

Use a solar reel (mounted at the pool's edge) or fold the cover neatly for storage. See the storage section below for specifics.

How to Trim a Solar Pool Cover for the Perfect Fit

A well-trimmed cover maximizes heat retention and is easier to handle than a loose, excess-material cover. Here's how to get the fit right.

For rectangular pools: Mark the pool perimeter on the cover from below while it floats on the water, then cut to that line. Leave ¼–½ inch inside the pool wall; don't cut to sit on top of the coping.

For irregular shapes (kidney, L-shape, freeform): Cut in stages. Start with the overall rectangular bounds, then make relief cuts into the curves. A flexible cover adapts to curves when cut this way; you're creating a series of flaps that conform to the shape rather than trying to cut a perfect curve in one pass.

For very large pools: Consider cutting the cover into 2–3 manageable sections rather than one large piece. Sections are easier to deploy, remove, and store. They also eliminate the safety concern of a single large cover that can billow around a person who falls in. Multiple sections can be lapped slightly at their edges to maintain full surface coverage.

Trimming tools: Sharp scissors work for most covers; a utility knife and straightedge work better for long straight cuts. Cut on a clean flat surface, not while the cover floats on the pool.

 

Bubble Side Up or Down? Proper Installation Explained

Bubble side down, always, for heating.

The bubbles face the water for three reasons:

1. Insulation: The trapped air in each bubble creates a thermal barrier between the cooler pool water and the ambient air, reducing overnight heat loss.

2. Heat transfer: The increased surface area of the bubble-textured side in direct contact with the water improves conductive heat transfer from the warmed plastic into the pool.

3. Solar absorption: The smooth top surface allows maximum solar radiation to pass through to the bubbles and water beneath.

The exception: Bubble side up if you're trying to cool the water (rare, but possible in very hot climates where pool water overheats). Bubbles facing up reflect heat back and reduce warming.

How to remember it: The bubbles should feel the water. Smooth side feels the sun.

When to Remove Your Solar Cover

Always remove before:

• Swimming; never allow swimmers to enter a covered pool

• Shocking the pool (see chemistry section)

• Adding any granular chemicals (they can sink into bubble pockets and cause localized concentration and discoloration)

• High-wind weather where the cover could be displaced and create a hazard

You can leave the cover on during:

• Automated pool cleaner cycles; robotic cleaners can operate under a cover

• Regular circulation pump operation; the pump runs normally with the cover on

• Adding liquid chemicals through the skimmer (some pool owners do this; dissolve in a bucket of water first and pour near the skimmer return)

 

How Solar Covers Affect Pool Chemistry

This is where most solar cover problems start and the section most guides skip.

Chlorine and the Solar Cover

A solar cover significantly reduces chlorine consumption by:

• Blocking UV radiation, which degrades chlorine (uncovered pools lose 50–90% of free chlorine to UV daily in direct sun)

• Reducing evaporation, which concentrates rather than depletes chemicals

• Keeping debris out, which reduces the organic load that consumes chlorine

The result: Pools with solar covers in consistent use often need 30–50% less chlorine to maintain the same free chlorine level. This is a benefit, but it requires adjusting your dosing routine rather than continuing at the same schedule.

Never Replace the Cover After Shocking

This is the most important solar cover chemistry rule. After shocking, free chlorine spikes to 5–10+ ppm. Replacing the cover while chlorine is this high:

• Bleaches and degrades the bubble material

• Can cause yellowing or discoloration that is permanent

• Traps high-concentration chlorine against the cover surface for extended periods

Per manufacturer guidance for solar covers: Allow free chlorine to return to 1–3 ppm before replacing the cover after any shock treatment. Test with test strips before covering. This typically takes 12–24 hours depending on the shock dose, sunlight, and pool volume.

Algae and the Solar Cover

A solar cover creates warm, still water on the pool surface, conditions that favor algae if chemistry is not maintained. Pool owners who get algae under their solar cover almost always have one of two problems:

• Free chlorine dropped below 1 ppm while the cover was on

• The cover was left on so long that circulation was inadequate

Prevention: Test chlorine under the cover every 2–3 days. Don't skip testing because the pool "looks fine"; algae establishes in clear water before it becomes visible. Run the pool pump daily for adequate turnover even with the cover on.

pH and Solar Covers

Solar covers reduce CO₂ off-gassing from the water surface, which can gradually raise pH over time. With consistent cover use, check pH weekly and be prepared to add muriatic acid more frequently than you would with an uncovered pool.

Best Ways to Store a Solar Pool Cover

Improper storage is the leading cause of premature solar cover wear, bubbles detaching, plastic cracking, and cover deforming are almost always storage-related, not manufacturing defects.

Option 1: Solar Reel (Best for Ease of Use)

A solar reel is a rolling tube mounted at one end of the pool on legs or a wall bracket. The cover attaches to the tube and rolls up when you turn the handle. This is the most convenient option; the cover goes on and off in under a minute.

Considerations: Reels cost 100–400+ depending on material (aluminum vs. stainless). The reel stays outdoors near the pool, which means the rolled cover is exposed to UV. Use a cover or UV-resistant bag to protect the rolled cover from UV degradation when stored on the reel.

Option 2: Fold and Store in a Shaded Area

If you remove the cover completely for storage, fold it loosely (don't crease sharply; this cracks the bubble material over time). Store in a shaded, cool location, such as a garage, shed, or under a deck. Keep away from pool chemicals, solvents, and petroleum products that can off-gas and degrade the plastic.

Before long-term storage: Rinse both sides with fresh water to remove pool chemicals, sunscreen residue, and minerals. Allow to dry completely before storing; moisture trapped in a folded, sealed cover promotes mold and bubble adhesion failure.

Storage container: A dedicated solar cover bag (sold by most pool supply retailers) or a large clean plastic storage bin with a lid works well. The container needs to be large enough to store the cover without sharp creases.

What Degrades Solar Covers in Storage

• Direct sun exposure: UV radiation without water contact degrades the plastic faster than water-contact operation

• Folding over sharp edges or corners: Creates stress lines that crack the bubble material

• Exposure to pool chemicals: Storing a cover near chlorine tablets, shock, or liquid acid dramatically shortens its life

• Wet storage in a sealed container: Promotes bubble failure and mold

Common Solar Pool Cover Mistakes to Avoid

Replacing the cover after shocking. The single most common cause of solar cover discoloration and bubble damage. Wait until free chlorine is below 3 ppm before covering.

Leaving a tablet floater under the cover. A chlorine tablet floater trapped under the cover concentrates chlorine in one spot on the cover surface, causing bleaching and discoloration. If you use a floater, remove it before covering the pool.

Not cutting the cover to fit. An oversized cover that drapes over the coping or sits on the deck edges creates leverage points that stress the cover and can pull it into the pool in wind. Cut to fit, it floats more securely, is easier to handle, and performs better.

Storing in direct sunlight. UV degradation is accelerated without water contact. A cover stored rolled-up in full sun will degrade in 1–2 seasons rather than the 3–5 year typical service life.

Skipping the pre-storage rinse. Pool chemicals left on the cover during storage continue degrading the plastic. Rinse before any storage longer than a few days.

Using the cover as a safety device. Solar covers are not safety covers. They will not support the weight of a child or pet. Never leave children or animals near a covered pool unsupervised, and don't assume the cover provides fall protection.

Not testing chemistry under the cover. "Out of sight, out of mind" is the solar cover trap. Chemistry needs to be tested even when the pool looks clean through the cover. Do it at least every 2–3 days.

 

Solar Cover vs. Solar Rings vs. Winter Covers vs. Safety Covers

Solar rings are modular discs (typically 5-foot diameter) that function similarly to a solar cover but don't require cutting or reeling. They're easier to handle individually but don't provide the same full-surface coverage as a fitted blanket. Good option for irregularly shaped pools where cutting a blanket to fit is challenging.

Winter covers are heavier, opaque covers designed for off-season protection, not heat retention. They block debris but don't provide the thermal and evaporation benefits of a solar cover.

Safety covers are ASTM F1346-rated covers anchored to the pool deck that can support the weight of a child or adult. They're the only pool cover type that provides genuine drowning prevention. Solar covers do not meet this standard.

 

How Much Heat Does a Solar Cover Add?

Per manufacturer guidance and field experience: a solar cover raises pool water temperature 10–15°F compared to an uncovered pool under the same conditions, measured after three consecutive sunny days.

Factors that affect heating:

• Sunlight hours and intensity (more sun = more heat)

• Ambient air temperature (warmer days = faster heating)

• Pool volume (smaller pools heat faster)

• Cover coverage percentage (full coverage outperforms partial coverage)

• Whether the cover stays on overnight (overnight retention is where much of the benefit accumulates)

On a single sunny day, you can expect 1–3°F of temperature increase per hour of full sun exposure with the cover on. The cumulative effect over consecutive days is where the 10–15°F figure comes from.

For guidance on running a pool heater alongside a solar cover for maximum efficiency, see our guide on whether to run a pool heater overnight. For a complete pool accessories checklist, see our essential pool care equipment list.

Frequently Asked Questions

Which side of a solar pool cover faces up?

The smooth side faces up; the bubble side faces down toward the water. The bubbles should touch the water, they trap air that insulates the water and increases heat transfer. Smooth side up maximizes solar radiation passing through to the water.

How long does it take a solar cover to heat a pool?

Most pool owners see a noticeable temperature increase within 6 hours on a sunny day. The full benefit (10–15°F above uncovered water temperature) typically accumulates after three consecutive sunny days with the cover left on overnight.

Can you shock a pool with the solar cover on?

No. Always remove the solar cover before adding shock. The high chlorine concentration from shocking bleaches and permanently discolors the cover material. Replace the cover only after free chlorine returns to 1–3 ppm,  typically 12–24 hours after shocking.

Can you cut a solar pool cover?

Yes, cutting to fit is standard practice and does not void the warranty. Cut with sharp scissors or a utility knife. Many pool owners cut large covers into 2–3 sections for easier handling.

How long does a solar pool cover last?

3–7 years with proper care. Storage is the biggest factor, covers stored in direct sun, near chemicals, or tightly folded without rinsing degrade significantly faster. Covers used and stored correctly regularly reach the upper end of this range.

Does a solar cover help with chemical costs?

Yes. By blocking UV radiation and reducing evaporation, solar covers reduce chlorine consumption by 30–50% in most pools. pH management frequency may increase slightly as CO₂ off-gassing is reduced.

Can solar covers cause algae?

They can contribute to algae if chemistry is neglected; the warm, still water under a cover is favorable for algae if chlorine drops below 1 ppm. Regular testing (every 2–3 days) and adequate pump runtime prevent this.

Related reading:

• Should I Run a Pool Heater Overnight?

• An Essential List of Pool Care Equipment