Pool domes and enclosures
A structure over the pool is the most literal way to stretch a season. One specification decides whether it warms the water or just keeps the leaves out, and half the category gets it wrong.
Quick picks
Ranked on shell transparency first, then on whether the maker publishes a fitment specification you can hold a tape measure against. Live prices come from the retail listing.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 |  Best overall PASBAS 18 ft Above-Ground Pool Dome Cover Transparent PVC on fiberglass rods, three anchoring methods, and the only listing that publishes how pool wall height changes the fit. | An 18 ft round above-ground pool where you want the water warmer, not just cleaner | |
| 2 |  Best documented fit EXIT Toys 12 ft Round Pool Dome Enclosure TUV-approved, with exact rail thickness, leg diameter and leg-count rules. 12 ft frame pools only. | A 12 ft round frame pool whose rail and leg dimensions you can measure | |
| 3 |  Best budget pick RIDFY 15 ft Round Pool Dome Cover for Frame Pools The cheapest one that still publishes a fit spec — and the only listing anywhere here that refuses to promise a temperature. | A 15 ft round frame pool on a tight budget | |
| 4 |  Best availability at 18 ft KEIKI 18 ft Retractable Pool Dome Enclosure Clear PVC on fiberglass, ships in a day or two. Its fitment line is 'most standard sizes', which is not a specification. | An 18 ft round pool when you want the dome this week | |
| — |  The one that will not warm your pool Alickwang Weatherproof Pool Dome Cover, 11-12 ft Round Excellent 600D opaque fabric, eight sandbags, sixteen tie-downs — and no sunlight reaches the water through it. | Keeping rain, leaves and pine needles out — not for warming the water | |
| 6 |  Buy this as well, not instead Sun2Solar 1600 Series Ultimate Blue Solar Cover A dome sits above the water. Only a floating cover sits on it, and the two do different jobs. | An inground pool you cover most nights, every season |
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
The number that makes the case for an enclosure
Almost nothing in the dome category argues for itself properly. The listings talk about leaves and rain. The strongest argument is a figure the Department of Energy publishes about something else entirely.
| A 7 mph surface wind raises energy consumption to 4x still air | DOE states a 300% increase |
| Evaporation is about 70% of a pool's total heat loss | DOE |
| An enclosure removes surface wind entirely |
This is a published figure about wind, not a published figure about domes — no manufacturer here cites it, and none of them publish a saving of their own. We are showing you the mechanism, not a measured result for any of these products.
That 4x is the whole idea. Wind does not just carry heat away by convection; it sweeps saturated air off the water surface and replaces it with dry air, which is what keeps evaporation running. A structure over the pool stops the wind reaching the surface and lets the air inside go humid, and both of those attack the same loss.
Our page on how fast a pool loses heat works through where the energy actually goes, and heating a pool in winter already makes the point that an enclosure does more than any equipment choice. This page is about which enclosure you can actually buy.
How we judged these
Four things, in this order.
- Is the shell transparent? This single question sorts the category into two products that are sold under one search term. A clear shell passes sunlight to the water and traps the warmed air above it. An opaque one does neither.
- Does the listing publish a fitment specification you can measure against? A dome that does not fit is a dome you return. Two of the five below publish rail and leg dimensions; one publishes how wall height changes the covered diameter; two say “fits most round pools”.
- Frame and anchoring. Fiberglass rods and staking hardware, or an unspecified frame and a hope.
- Is it actually purchasable today? Two of the best-known products in this category failed this and are discussed below rather than ranked.
We did not rank on claimed temperature gain, because with one honorable exception nobody in this category publishes one that means anything.
Two products, one search term
This is the finding to take away even if you buy nothing. Search “pool dome” and you will be shown two different objects with near-identical listings, photographs and prices.
| Type | Shell | What it does | What it does not do |
|---|---|---|---|
| Transparent dome | Clear PVC film over rods | Passes sunlight to the water, traps warmed humid air, blocks wind, keeps debris out | Nothing much in winter — it is a summer structure |
| Opaque weather dome | Coated fabric, often 600D Oxford, usually black | Sheds rain, blocks debris, survives weather well | Warm the water. No light reaches it |
| Net dome | Mesh | Keeps leaves and insects out | Block wind, trap heat or pass a useful amount of sun |
All three are sold as a 'pool dome cover'. Only the first one belongs on a site about stretching the swim season, and it is not always the one at the top of the search results.
Fitment is the hard part, and most makers dodge it
A floating solar cover is forgiving: it is sold oversized and you trim it. A dome is a rigid arc with a fixed footprint, and it either lands on your pool’s rail or it does not.
| Dome | Fitment specification published |
|---|---|
| EXIT Toys 12 ft | Round top rail no thicker than 1.97 in; round legs no larger than 1.57 in diameter; an even number of legs; pool diameter 142 to 145.5 in |
| RIDFY 15 ft | Round top rails up to 1.968 in; round legs up to 1.5 in diameter; an even number of legs |
| PASBAS 18 ft | A compatibility chart across pool wall heights from 1.64 to 6.23 ft, with covered diameter falling as the wall gets taller |
| KEIKI 18 ft | “Compatible with most standard sizes of above-ground pools” |
| Alickwang 11-12 ft | “Perfect for diameter 11-12 ft above ground circular frame pools” |
The top three are specifications. The bottom two are hopes. That is not a reason to avoid the bottom two outright, but it is a reason to measure carefully and to buy where returns are easy.
The PASBAS line is the one worth understanding, because it applies to every dome whether or not the maker mentions it. A dome is an arc of fixed length. The taller your pool wall, the higher up that arc has to start, and the smaller the circle it can enclose — so an “18 ft” dome covers less than 18 ft on a 52 in wall and more on a 30 in one. PASBAS is the only listing we read that says this out loud.
The other fitment rule, from EXIT and RIDFY: an even number of legs. Dome straps anchor in opposing pairs, and an odd-legged frame pool leaves one strap with nothing to pull against.
What we excluded, and why
- The Bestway 58612 round dome — the only established pool brand in this category, and it fails twice. Its construction is 2-layer UPF 50+, which means it is deliberately engineered to block ultraviolet light: a shade structure, not a solar one. And its availability line when we checked read “usually ships within 6 to 7 months”. Worth knowing about, not worth recommending. Note also that the 19 ft 8 in dome is stated as fitting pools up to 16 ft, which is the arc-length effect again.
- Net domes — the Flexnet Dome for 16 to 18 ft pools is sold explicitly as “6 of 7 parts”, with the PVC Schedule 40 support poles not included and to be bought by the customer. It is also a mesh, sold for keeping the pool “clean and bug free”. It does not trap heat and does not pretend to.
- Inflatable air-supported domes at roughly $1,100 to $4,800 — these are a genuinely different product, and on paper the most effective thing in this article: a sealed, blower-inflated structure over the whole pool. We could not rank one. The listings we read carry no identified brand, and on the representative $1,099 unit the entire published specification is the single line “Material: PVC”. There is nothing there to write an honest paragraph from, let alone spend four figures on.
A dome is not a cover, and it does not replace one
This is where we part company with most of the category’s marketing. A dome sits above the water on a frame. A solar cover sits on the water. They attack the same loss by different routes and they stack.
| Transparent dome | Floating solar cover | |
|---|---|---|
| Stops wind reaching the surface | Yes, completely | Yes, where it covers |
| Seals the water surface | No — humid air still sits above it | Yes |
| Passes sunlight to the water | Yes, minus what the film absorbs | Yes |
| You can swim with it in place | Yes, that is the point of the headroom | No |
| Keeps debris out | Yes, and better than a cover | Yes |
| Typical outlay | Low hundreds | Tens to low hundreds |
The row that matters is the second one. A cover physically caps the surface; a dome raises the humidity above it and removes the wind. Both reduce evaporation, and a pool with both loses less than a pool with either.
If you are choosing between them on a budget, buy the cover first every time — it is cheaper, it seals the surface outright, and our payback arithmetic works it through. The dome is the second purchase, and what it buys that a cover cannot is that you can swim under it.
The honest limits
- Wind loading is the failure mode. A dome is a large, light, sealed shape in an open yard, and none of these listings publish a wind rating. Stake it properly, and take it down before a storm rather than after one.
- It is not a safety barrier. Nothing here is a safety cover, none is rated to hold a person’s weight, and a dome over a pool can read as more secure than it is. Our comparison of cover types covers what a safety cover actually is.
- Snow is a different problem. These are summer and shoulder-season structures. None publishes a snow load, and the fabric weather domes are the only ones built to shed anything heavy.
- A sealed clear dome in full sun gets hot and humid. That is the mechanism working, and it also means condensation, and warm still water is friendlier to algae. Ventilate it on hot days and keep your chemistry honest.
- Nobody publishes a temperature gain we would repeat. Not one manufacturer here states a measured figure with conditions attached. The RIDFY listing is the only one that declines to print a number at all, and we think that is the correct position rather than a weakness.
Who should buy one
- Anyone with an above-ground pool on an exposed, windy site. The DOE wind figure is doing the work here, and a windbreak you can swim inside is a large intervention for a few hundred dollars.
- Anyone chasing April and October. This is the season-extension purchase in its most literal form, and it stacks on top of everything in stretching the swim season.
- Anyone tired of skimming. Debris exclusion is the benefit the listings lead with, and it is real.
Who should not
- Anyone with an inground pool. Every product here is built for a round above-ground pool with a rail to anchor to. Inground enclosures exist and are a contractor purchase, not a shopping-cart one.
- Anyone without a cover yet. Cheaper, simpler and it seals the surface. Start there and see where the water settles — our overnight heat-loss page explains how to measure the difference yourself.
- Anyone whose pool is not round, or is over about 24 ft. The category effectively stops there.
What we could not assess
How many degrees any of these adds to a real pool, because no manufacturer publishes a figure with conditions and we do not test. What wind speed a properly staked dome survives, since none publishes a rating. How the PVC shells hold up across a second and third summer of ultraviolet. And whether the inflatable class at four figures is worth it, because the listings publish almost nothing about it.
Every pick, in detail
What each one publishes, what is good and bad about it, and — the section this category usually omits — what we could not judge without owning one.
PASBAS 18 ft Above-Ground Pool Dome Cover
The transparent dome we would buy at 18 ft, and it earns that on one bullet nobody else prints: PASBAS states that the dome's covered diameter changes with your pool's wall height, and publishes a compatibility chart across wall heights from 1.64 to 6.23 ft. That is the specification that decides whether a dome fits, and it is the one the rest of this category replaces with 'fits most round pools'. Flexible fiberglass rods, rust-proof metal brackets and three anchoring methods for lawn, deck or concrete.
Best for An 18 ft round above-ground pool where you want the water warmer, not just cleaner
| Shell material | Transparent PVCTransparent is the whole point. An opaque dome keeps rain off and keeps sun out, which is the opposite of what a heat buyer wants. | Manufacturer |
|---|---|---|
| Frame | Internal flexible fiberglass rods with rust-proof metal brackets | Manufacturer |
| Fit | 18 ft nominal, with covered diameter falling as pool wall height rises across a stated 1.64 to 6.23 ft rangeA dome is a fixed arc. The taller your pool wall, the higher up that arc has to land, and the smaller the circle it encloses. PASBAS is the only listing in this group that says so. | Manufacturer |
| Anchoring | Three methods — soft ground, wood deck, or concrete patio | Manufacturer |
| Operation | Umbrella-style hinge with heavy-duty straps, stated as a one-person job | Manufacturer |
- The only dome here that publishes how wall height changes the fit
- Fiberglass rods and metal brackets rather than an unspecified frame
- Three anchoring options, so a deck installation is not an improvisation
- No published wind rating, snow load or material thickness
- No warranty term stated anywhere on the listing
- PASBAS has no service record we could check
- How the PVC shell holds up to a second and third season of UV
- What wind speed it actually survives when properly staked
- Whether the compatibility chart matches the delivered product
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
EXIT Toys 12 ft Round Pool Dome Enclosure
The best-documented product in a category that documents almost nothing. EXIT publishes an exact fitment specification — round top rail no thicker than 1.97 in, round legs no larger than 1.57 in in diameter, an even number of legs — and it is TUV-approved, which is the only third-party certification we found anywhere in this group. The trade is that those numbers are a filter: if your frame pool's rail is fatter or its legs are odd-numbered, this dome does not fit and the listing tells you so rather than letting you find out on the lawn.
Best for A 12 ft round frame pool whose rail and leg dimensions you can measure
| Shell material | Transparent PVC | Manufacturer |
|---|---|---|
| Certification | TUV-approvedA third-party mark rather than a self-declaration. Nothing else in this group carries one, which does not make the others unsafe — it makes them unverified. | Manufacturer |
| Fit | Round top rail no thicker than 1.97 in; round legs no larger than 1.57 in diameter; an even number of legs; pool diameter 142 to 145.5 inThe most precise fitment specification in this category by a wide margin. Measure before ordering — these are a filter, not a guideline. | Manufacturer |
| Operation | Secure straps with a hinge mechanism | Manufacturer |
- TUV-approved — the only third-party certification we found in this category
- Publishes rail thickness, leg diameter and leg count rather than 'fits most pools'
- The cheapest way into a dome if your pool is a 12 ft frame pool
- The precise fitment rules it out for most steel-wall and soft-sided pools
- 12 ft only — it does not scale to the commoner 15, 18 and 24 ft rounds
- No wind rating, material thickness or warranty term published
- What the TUV approval actually covers on this product
- Service life of the PVC in strong sun
- How it behaves in a storm once staked
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
RIDFY 15 ft Round Pool Dome Cover for Frame Pools
The cheapest dome here that still publishes a real fitment specification, and the only listing in the whole category that declines to promise a temperature. RIDFY words its warming claim as supporting seasonal swimming 'without promising a fixed temperature increase' — which, in a category where every other product prints a number it cannot support, is worth noticing. Same rail-and-leg fit rules as the EXIT dome, at 15 ft rather than 12.
Best for A 15 ft round frame pool on a tight budget
| Shell material | Clear PVC | Manufacturer |
|---|---|---|
| Fit | 15 ft round frame pools; round top rails up to 1.968 in; round legs up to 1.5 in diameter; an even number of legsEssentially the same filter as the EXIT dome, one size up. RIDFY repeats it twice on the listing, which suggests returns. | Manufacturer |
| Weight | 50.7 lb | Retail listing |
| Temperature claim | None — the listing explicitly declines to promise a fixed temperature increaseThis is the only product on this site, in any category, whose own listing refuses to print a temperature number. It is the correct position and almost nobody takes it. | Manufacturer |
- By some distance the cheapest dome that publishes a fitment specification
- Refuses to make a temperature claim it cannot support
- Covers the 15 ft size that the EXIT dome does not reach
- Stock has been thin every time we have checked
- Same frame-pool-only fit restriction as the EXIT dome
- No frame material, wind rating or warranty stated
- Shell thickness, which is not published
- Whether the frame is fiberglass or steel
- Longevity of a budget PVC shell outdoors
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
KEIKI 18 ft Retractable Pool Dome Enclosure
The 18 ft transparent dome with the best availability, and the one to take if the PASBAS is out of stock. Clear PVC film over fiberglass rods, strap-and-hinge operation, ships in a day or two. The reason it is not the first pick is the fitment line: KEIKI says only that it is 'compatible with most standard sizes of above-ground pools', which is the phrase this category uses when it has not measured anything.
Best for An 18 ft round pool when you want the dome this week
| Shell material | Transparent PVC film | Manufacturer |
|---|---|---|
| Frame | Fiberglass rods | Manufacturer |
| Fit | Stated only as 'compatible with most standard sizes of above-ground pools'No rail dimension, no leg spec, no wall-height chart. Measure your pool and be prepared to return it. | Manufacturer |
| Stated dimensions | 216 x 216 x 108 in | Retail listing |
- Best stock position of the 18 ft domes when we checked
- Transparent shell and fiberglass rods, the right construction for warming
- Straps and hinge, so it opens without full removal
- 'Fits most pools' is not a fitment specification
- No anchoring hardware detail published
- New listing with no history to judge
- Whether it fits your specific pool, because the listing does not say
- Film thickness and frame gauge
- Durability, on a listing first published in 2026
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
Alickwang Weatherproof Pool Dome Cover, 11-12 ft Round
Included as the counter-example, because it is the shape people buy by mistake. This is a well-made dome — 600D Oxford fabric, PVC-coated liner, double-needle stitching, sealed seams, four poles, eight sandbags and sixteen tie-downs, which is more anchoring hardware than any transparent dome here ships with. It is also OPAQUE and black. It sheds rain and keeps leaves out extremely well, and it will not warm your pool, because no sunlight reaches the water through it. If that is what you want, buy it. If you came here to stretch the season, it is the wrong product.
Best for Keeping rain, leaves and pine needles out — not for warming the water
| Shell material | Opaque black 600D Oxford fabric with a waterproof PVC-coated liner600 denier is a genuine specification and a good one. It is also completely opaque, which is the entire reason this is not a heating product. | Manufacturer |
|---|---|---|
| Construction | Double-needle stitching with sealed seams | Manufacturer |
| Anchoring | 4 reinforced support poles, 8 weighted sandbags, 16 tie-down ropesMore anchoring hardware than any transparent dome in this roundup ships with. | Manufacturer |
| Shape | Curved dome that sheds rainwater instead of pooling it | Manufacturer |
| Solar warming | None claimed, and none possible through an opaque shell | Manufacturer |
- Publishes a real fabric denier, which the transparent domes do not
- The most complete anchoring kit in this roundup
- Sheds rain properly rather than forming a water pocket
- Opaque — it blocks the sunlight that would have warmed the water
- 11-12 ft only, the smallest size bracket here
- The listing's part number reads 14FT while the title says 11-12FT
- Whether the part-number discrepancy indicates a listing error or a variant
- How the black fabric affects water temperature in practice
- Coating life on the PVC liner
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
Sun2Solar 1600 Series Ultimate Blue Solar Cover
The cover to buy if you intend to keep using it in five years. 16 mil is the thickest tier the category sells, and thickness on a solar cover buys durability rather than heat — Bob Vila measured every cover in its hands-on group at the same 4 to 5 degrees, from 12-mil clear to 16-mil blue. Pay the extra for the one that survives being dragged over the coping twice a day, not for a temperature difference that did not show up in the only published one-hour test in this category.
Best for An inground pool you cover most nights, every season
| Price shown for | 24 ft roundThis product is sold in several sizes on one listing. The live price and photograph on this page are the ones Amazon returns for this variant; other sizes are priced separately. | Retail listing |
|---|---|---|
| Thickness | 16 milThe manufacturer publishes no retrievable specification sheet; figure is as listed at retail. | Retail listing |
| Color | Blue | Retail listing |
| Stated lifespan | 5 to 10 years for the 16-mil tierSwim University's published figure for 16-mil covers generally, not a Sun2Solar warranty statement. | Retail listing |
| Bubble side | Bubbles face the waterCategory-wide instruction, not brand-specific. The bubbles are the insulating layer and they have to touch the water. | Published standard |
4 to 5 degrees F in one hour
Claimed by Bob Vila, measured across all covers in their group. Conditions: One hour under 2pm sun on 89 to 92 degree F days. Source
Their figure was the same for every cover they put on the water. Read our reconciliation of what a one-hour reading actually measures before you plan around this number.
- Thickest tier sold, which is where the durability difference actually is
- Blue absorbs more of the incoming energy at the surface than clear does
- Cuts oversize to your pool shape with household scissors
- Heavy and awkward at 16 mil — a large inground cover is genuinely a two-person job without a reel
- Costs meaningfully more than the 12-mil version for no measured heating advantage
- Whether the seams hold up over five seasons of daily handling
- How the bubble layer survives repeated dragging over rough coping
- Whether the stated lifespan tier holds for this specific product line
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
Questions people actually ask
Do pool domes actually heat the water?
Will a pool dome fit my pool?
Can you swim with the pool dome on?
Is a pool dome better than a solar cover?
Do pool domes survive wind?
Are inflatable pool domes worth it?
- U.S. Department of Energy pool-energy figures (evaporation share, BTU per pound evaporated, cover savings, recommended temperatures, wind effect)Recreonics, reproducing and attributing the U.S. Department of Energy · read 2026-09-02
- U.S. Department of Energy, Energy Saver: Swimming Pool Covers (archived — the live page now returns 404)U.S. Department of Energy via the Internet Archive · read 2026-09-02
- PASBAS 18 ft pool dome listing: transparent PVC shell over flexible fiberglass rods and rust-proof metal brackets, three mounting methods (soft ground, wood deck, concrete), umbrella-style hinge, and a stated compatibility chart in which the covered diameter falls as pool wall height rises from 1.64 ft to 6.23 ftPASBAS, as listed at retail · read 2026-09-21
- EXIT Toys 12 ft pool dome listing: TUV-approved, transparent PVC, and an exact fitment specification - round top rail no thicker than 1.97 in, round legs no larger than 1.57 in diameter, an even number of legs, pool diameter 142 to 145.5 inEXIT Toys, as listed at retail · read 2026-09-21
- RIDFY 15 ft pool dome listing: clear shell, 50.7 lb, fitment stated as round top rails up to 1.968 in, round legs up to 1.5 in diameter and an even number of legs, and a warming claim worded as supporting seasonal swimming 'without promising a fixed temperature increase'RIDFY, as listed at retail · read 2026-09-21
- KEIKI 18 ft pool dome listing: transparent PVC film over fiberglass rods, strap and hinge closure, fitment stated only as 'compatible with most standard sizes of above-ground pools'KEIKI, as listed at retail · read 2026-09-21
- Alickwang 11-12 ft pool dome listing: OPAQUE black 600D Oxford fabric with a waterproof PVC-coated liner, double-needle stitching and sealed seams, 4 support poles, 8 weighted sandbags and 16 tie-down ropes - sold for rain and debris shedding, with no solar warming claim madeAlickwang, as listed at retail · read 2026-09-21
- Bestway 58612 round pool dome listing: 19 ft 8 in x 19 ft 8 in x 9 ft 8 in, stated as compatible with above-ground pools up to 16 ft in diameter, 2-layer UPF 50+ construction with 8 transparent windows and 2 entry points, 30 minute setup, and an availability line of 'usually ships within 6 to 7 months'Bestway, as listed at retail · read 2026-09-21
- Flexnet Dome pool net dome listing for 16-18 ft pools: a mesh dome sold for keeping the pool clean and bug free, shipped as '6 of 7 parts' with the PVC Schedule 40 support poles explicitly not included and to be bought separately by the customerFlexnet Dome, as listed at retail · read 2026-09-21
- Representative inflatable pool dome listing at about $1,099: brand recorded as Generic, ships in 2 to 3 weeks, and the entire published specification is the single line 'Material: PVC'Listed at retail under no identified brand · read 2026-09-21
#ad Where a retailer’s listing is cited above as the source of a published specification, that link is an affiliate link, at no extra cost to you. Independent sources and manufacturer documentation are never wrapped and earn nothing. How this site is funded.
Every URL above was fetched and returned content on the date shown. Where a figure is ours rather than somebody else’s, the arithmetic is on the page and on the methodology page. If you find an error in it, we would genuinely like to know.
Read next
Stretching the swim season
What actually adds weeks at each end of the season, why the shoulder season is a different problem from midsummer, and the order to spend in.
Heating a pool in winter
Why winter heating is not summer heating with a bigger bill: the gap widens, heat pumps fade, wind and evaporation both rise, and freeze protection becomes the real constraint.
How fast a pool loses heat
Evaporation, radiation, convection and conduction, with the arithmetic on what each night actually costs and a measurement you can take yourself.
Keeping a pool warm overnight
The specific problem of overnight heat loss: what causes it, what each fix is worth, and the order to try them in.
Solar covers for above-ground pools
Why fit matters more than thickness on an above-ground pool, and the arithmetic showing why a small pool responds several times faster to the same sunlight.