Pool Cover On or Off During the Day? What to Do and When
Pool cover on or off during the day is a common question among Australian pool owners, and the answer depends on the conditions.
Leaving the cover on around the clock can cause chlorine spikes, a strong odour or algae under the blanket. Removing it every morning exposes the water to heat, evaporation and chemical loss.
This guide sets out a routine for each situation, along with solutions to the most common chlorine and algae problems, for any swimming pool cover.
Pool Cover On or Off During the Day: The Quick Answer
For most pools, the cover should be on whenever the pool is not in use. A small number of situations require its removal.
Keep It Off When…
- A heatwave is pushing the water temperature too high. Overheated water depletes chlorine and increases the risk of algae.
- The pool has just been shocked. Leave the cover off until chlorine is at or below 2.5 ppm.
- The pool needs to breathe. A few hours uncovered each week allows trapped gases to escape and gives an accurate test.
- An opaque cover is fitted to an unheated pool and direct sun on the water is required.
Keep It On When…
- The pool is not in use. A solar pool cover collects the sun's heat and transfers it into the water, and Elite's solar range stops up to 98 to 99.84% of evaporation.
- Conditions are cool, windy or cloudy, when open water loses heat quickly.
- The household is away or the pool is idle, provided the chlorinator output is reduced.
General rule: Owners differ; most keep it on except when swimming. Keep the cover on by default and remove it for swimming, shock treatments, extreme heat and regular airing. Elite's guide on how to protect your pool cover from heat damage sets out the care requirements.
Day, Night, Heatwave, Away, Winter: Your Cover Routine
The answer to pool cover on or off during the day changes with the weather and the season. Use the routine below, then adjust it to the results of regular water tests.
| Situation |
Cover On or Off |
Why |
Tip |
| Sunny day, no swimmers |
On |
A solar cover turns sunlight into water heat and stops evaporation |
Remove the cover fully before swimming |
| Cool, windy or cloudy day |
On |
Cool air and wind draw heat out of open water quickly |
Check clips and straps so wind cannot lift the cover |
| Night |
On |
Open water loses heat quickly once the sun goes down |
Replace the cover after the last swim |
| Above 38°C, including 40°C days |
Off on the hottest days |
Elite's care guide advises removing covers when air or surface temperatures exceed 38°C |
Store it rolled, under a reflective over-cover, in full shade |
| Away for a week or more |
Usually on |
Keeps debris out and slows water loss |
Reduce chlorinator output and test before departure |
| Winter |
On, with regular checks |
Covering the pool over winter reduces debris and evaporation |
Lift it every one to two weeks to test and check for algae |
| Rain |
On |
Covers are designed for outdoor use in all weather |
Sweep pooled water off before rolling it up |
| Straight after shocking |
Off |
High chlorine damages cover material |
Test chlorine before replacing the cover |
Owners differ on covering the pool while away. Most leave the cover on so the pool stays clean and loses less water. Some prefer it off for long trips, so chlorine cannot build up under a sealed cover while nobody is checking.
Both approaches work with the correct setup. With the cover on, switch the chlorinator to cover mode or reduce its output, and set the pump timer. With the cover off, leave the chlorinator at its normal setting, check stabiliser levels and expect more leaves. Test the water on the day of departure and the day of return.
Owners with rigid slat covers have an advantage here, because the slats shed rain and debris rather than collecting them.
Winter is the other extended period. A solar cover can stay on through the cooler months, but if the pool sits idle from May to September, a winter pool cover is built for long periods and heavy leaf fall.
A solar cover is not a safety cover. Even a load-rated cover never replaces a pool fence and active supervision.
Does the Pool Heat Better With the Cover On or Off?
When owners weigh up pool cover on or off during the day, heating is usually the deciding factor. With a solar cover, keep it on.
A solar pool blanket works like a lid on a saucepan. The bubbles trap the sun's heat and transfer it into the water, while blocking the evaporation that carries heat away. Elite's solar covers add up to 6 extra weeks of swimming, and they work with gas, solar and heat pump heating.
Elite's automatic pool covers work on the same principle. The Aquaroll's polycarbonate slats let sunlight through to warm the water by day, then the trapped air in each slat insulates the pool overnight.
A thermal pool cover serves a different purpose. Elite's thermal range uses 5 mm or 3 mm closed-cell foam inside UV and chemical resistant polyethylene, which insulates better than a bubble cover. It is built to hold heat in a heated pool rather than collect sunlight.
Because foam does not gather sun the way bubbles do, some owners of unheated pools remove a pool thermal blanket on warm, sunny days and replace it before evening. For a heated pool, leaving it on is recommended.
A non heating pool cover does the opposite. Elite's non-heating range blocks sunlight so the water does not warm up, which also slows algae growth. Elite recommends these covers for shaded pools, cooler climates and pools with alternative heating. Leave one on during the day when keeping the water cool is the goal.
A cover can make a pool too warm. A run of hot days under a solar cover can make the water very warm, and sanitiser is then used up quickly. WA Health advises checking pools more often in hot weather, especially once the water is warmer than 25°C.
If the pool overheats every summer, consider covers that keep the sun out instead of a solar blanket.
When the cover is removed in a heatwave, do not leave it rolled up in the sun. Heat builds up inside the roll, which causes covers to shrink or burn. Elite's guidance on how to stop a cover shrinking or curling explains why partial shade is not sufficient.
Why Chlorine Spikes or Will Not Hold With the Cover On
Sunlight breaks chlorine down, and a cover shields the water from much of it. Elite's solar covers are designed to reduce chlorine loss in this way. If the chlorinator remains on its uncovered summer setting, levels can climb well above what is required.
Chlorine that will not hold is usually a separate problem. Warm water with low stabiliser, high phosphates or weak circulation depletes sanitiser, with or without a cover. Elite's guide to pool water chemistry sets out the stabiliser and phosphate levels that keep chlorine effective.
Elite's cover-care advice is to keep free chlorine at or below 2.5 ppm while a cover is on, with pH between 7.2 and 7.6. High chlorine and pH swings damage cover material. Elite's care guide notes that heat shrinkage is not covered under warranty.
Use Cover Mode or Turn the Chlorinator Down
Many salt chlorinators have a cover or reduced-output setting for this purpose. Where the unit has one, enable it whenever the cover stays on for extended periods. Where it does not, lower the output percentage or shorten the run time, one step at a time.
Test every few days until the setting holds steady. Keep the filter running while the cover is on so treated water continues to circulate. A robotic cleaner can run with the cover on. Balancing your water chemistry first makes this considerably easier.
Never Leave a Floating Chlorinator Under the Cover
A floater dissolves tablets at the surface. Under a cover it can remain in one spot, pressed against the plastic, with nowhere for the concentrated chlorine to disperse. This can bleach and weaken a section of the cover and push chlorine far above the safe range for the cover.
Remove the floater before the cover goes on. Alternatively, ask a pool specialist about a feeder that suits a covered pool.
Algae Under the Blanket (and Why Mineral Pools Are Prone)
Algae under a cover usually appears as slimy patches on the underside, or a green tinge around steps and corners. It requires warmth, nutrients and insufficient sanitiser. A warm, covered pool with the chlorinator turned right down provides all three.
Mineral and magnesium pools tend to run lower salt levels, and many owners keep chlorinator output low for softer water. That leaves less margin for error. A covered summer week with weak circulation can allow algae to establish before it is noticed.
To treat it, remove the cover, brush the walls and steps, test the water and raise the chlorine level. Leave the cover off until levels settle, then hose the underside before replacing it. For severe cases, Elite's step-by-step guide shows how to fix a green pool.
To prevent a recurrence, keep phosphates low, run the filter long enough in warm weather and brush while the cover is off. Leaves rotting on the cover and washing in are a major part of why a pool turns green, so sweep the cover before rolling it.
Should the Pool “Breathe”? Taking the Cover Off for a Few Hours
Yes, periodically. Chlorine and other chemical gases can build up in the gap between the water and the underside of the cover, especially in hot weather or when circulation is low. That trapped air is what is meant by letting the pool breathe.
These concentrated gases damage the cover and can distort test readings. Removing the cover releases these gases before readings are taken. Any routine for deciding whether to keep a pool cover on or off during the day should include this regular airing.
A simple routine is to leave the cover off for a few hours once or twice a week while the filter runs. Add liquid chlorine or acid during that window, and allow it to circulate before replacing the cover.
The easier the cover is to move, the easier this routine is to maintain. Pool cover rollers allow the cover to be wound off and on without dragging it across the coping.
A pool roller also holds the cover clear of the ground while the pool airs.
FAQs
Should I Put a Pool Cover On When It Rains?
Yes. Rain does not harm the cover, and keeping it on stops leaves and dirt washing in. Heavy rain can still raise the water level and dilute chemicals, so test the water after a heavy downpour. The exception is hail, or when sustained winds exceed 60 km/h. In these conditions, Elite's care guide recommends removing the cover and storing it securely.
What Are the Downsides of Using a Pool Cover?
Mainly effort and upkeep. A cover must be removed for every swim, and it requires protected storage when it is off. Covers also wear over time, faster if they are left in the sun or exposed to strong chlorine.
Is It Better to Run a Pool During the Day or Night?
For most pools, run at least part of the filter cycle during the day, when sunlight is breaking down chlorine and circulation prevents warm spots forming. Night running can be cheaper on off-peak power, so some owners split the cycle.
When Should You Put a Pool Cover On?
As soon as the last swimmer leaves the pool, ideally before the sun moves off the water. Allow added chemicals to circulate before covering, as set out above. In spring, covering early helps the water warm sooner.
Final Thoughts
In most conditions, the cover should stay on. When deciding whether to keep a pool cover on or off during the day, remove it for swimming, after shocking, on the hottest days and for a few hours each week to air the pool. Reduce chlorinator output to match, keep floaters out from under the cover and store it correctly when it is off.
Elite's full range of pool covers Australia owners can choose from is grouped by purpose: heat, debris, safety and automation.
Get an Elite Pool Covers Quote Today
Need specific pricing for your pool? Elite Pool Covers has designed and made pool covers, blankets and rollers in Australia since 1989. Call us on (08) 9240 2262 or request a personalised quote, to receive accurate pool cover pricing tailored to your unique requirements.