Yet another solar cover On or Off during the day thread

syntax53

Silver Supporter
Apr 12, 2016
77
Philadelphia, PA
I've read countless threads on various forums, as well as many web pages on the topic. The general consensus I get from this forum is, leave it off during the day if it's sunny, hot, and there's little to no wind.

However, I've also read plenty of people claiming they get better results leaving it on during the day. Even to the extremes of people claiming it gets so warm that they end up having algae issues. An argument to it is that it only heats the top layer of the pool. But what if I leave the pump running? Then it will circulate.

Yesterday, the first day of a heat wave, the water started out about 66 and ended at 68-69. I put the cover on for the first time last night and took it off this morning about 10am. After the second day of heat wave (low 90s) it got up to 70.

Has anyone done any studies on this? I've read enough opinions to make my head explode. Would love to see some real testing on the matter. Tomorrow is another and last day in the low 90s here. Tempted to leave it on and see what happens. It's the last day of heat wave though and we are having a pool party for Father's Day so I don't want to lose valuable heating.
 

camueller

Well-known member
May 11, 2016
492
Troy IL
from what I've read on the subject, it really doesn't matter one way or the other. Do whatever you want. In my case, I'm lazy, I only remove my solar blanket if I'm going to swim. That happens to be most every day. But during the week, I leave it covered all day when I'm at work and it is only uncovered for an hour or two while we swim after/before dinner. On the weekend I uncover in the morning and leave uncovered until the nighttime unless the weather is such that no one wants to swim.

The most important thing is that the pool is covered at night and when the temp/humidity is low
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
43,260
Tucson, AZ
Like you said at the beginning, cover on during the day retains the heat if there is any wind or you have low humidity.
 

Veccster

Bronze Supporter
Aug 30, 2016
357
Pittsburgh PA
I thought cover on during sunny days also saves on chlorine use and reduces evaporation.

Anyway, the water directly below my cover gets HOT. So I've turned the return jets upward to move that water and try to get some circulation. This is where a floor drain would be helpful (I don't have one).

+1 on the 'too lazy to remove even if there was an advantage to doing so'
 

Catanzaro

Platinum Supporter
TFP Guide
Jul 30, 2014
3,376
Monmouth County, New Jersey
My experience with the solar cover is as follows:

In my pool, the cover must be kept on for at least 2 days before the temperature of the water increases by about 5 degrees, which is all I need. Any longer than this, and my PH drops pretty quickly below the norm. Some people have reported that they have had issues with algae, but this could be due to circulation issues. With my pool, I do not as the rotating heads help a lot. In addition, suction from the skimmers is slows down a lot.

And yes, the chlorine consumption is cut down to about 1/3 to 1/2 of the normal usage and there is less evaporation with the cover on. I have also had very good success with putting the cover on at night and removing a few hours before swimming activity during the day, allowing the sun to beat down on the water.

My cover was cut in 1/2 + the steps. Then I took a 1" schedule 40 pvc, glued them together to about the with of the pool and rolling the cover off is a breeze. Easy to pick up and tuck away somewhere. You have to figure out what works for your cover and pool.
 

syntax53

Silver Supporter
Apr 12, 2016
77
Philadelphia, PA
Well I left it on today while I am at work. Everything between yesterday and today should be pretty equal with the only differences being that the water temp will start out 1-2 degrees higher than yesterday and the cover is left on during the day. It's expected to be about the same temp & humidy today as it was yesterday. My pump is left on the same schedule as well (low speed from 6-9am, full speed from 9am-5pm, low from 5-9pm). Will post results.
 

syntax53

Silver Supporter
Apr 12, 2016
77
Philadelphia, PA
Verdict is.... cover on!. At 5:30am this morning the temperature was 70 and it was 74 when I got home today. Pushing 75 to be honest, but we'll call it 74. So I got 4 degrees of temperature rise today with the cover on all day, pump running its normal schedule. First two days of the heat wave with the cover off I got 2 degrees each day and today I got 4. Used a lot less chlorine to boot. Temp, humidity, and wind level today were all very close to yesterday.
 

RoxxW

Well-known member
Dec 14, 2016
122
Poquoson, VA
So the cover can be in place while the pump is running? The return doesn't force it out of shape?

Verdict is.... cover on!. At 5:30am this morning the temperature was 70 and it was 74 when I got home today. Pushing 75 to be honest, but we'll call it 74. So I got 4 degrees of temperature rise today with the cover on all day, pump running its normal schedule. First two days of the heat wave with the cover off I got 2 degrees each day and today I got 4. Used a lot less chlorine to boot. Temp, humidity, and wind level today were all very close to yesterday.
 

syntax53

Silver Supporter
Apr 12, 2016
77
Philadelphia, PA
So the cover can be in place while the pump is running? The return doesn't force it out of shape?
Not at all for me. I'm sure it depends on how you have your jets pointed. I have 2 return jets + 1 old vacuum port that I now use as a 3rd return. My regular returns are pointed so that they just barely create a ripple on the surface, with my other pointed slightly down. My pool is also roughly 40x16 which could make a difference as well.
 

Green Goblin

Gold Supporter
Nov 5, 2012
92
Tennessee
I don't know of any real studies on this, but there is a lot I don't know...

My anecdotal experience-- used a solar cover for about 5 years, left it on all the time, seemed to work better that way. Now that I've moved and don't have a real pool at present I fill up a kiddy pool for the kids most weekends in TN. The water out of the hose is pretty cold to start with, and I put a thin clear plastic sheet (painters drop cloth type) over the pool and it seems to heat up much faster that way.

Found this out by accident, one day right after I filled the pool up, the lawn service showed up and I didn't want a bunch of grass in the kiddy pool. Had an unused drop cloth on hand, so put it on. With the pool in full sun, without the plastic cover it would still seem cool at the end of the day, with the plastic cover, it was comfortably warm within 2-3 hours.

None of this is even remotely scientific, but my suspicion is that the cover reduces evaporative cooling markedly, and that would seem to be the biggest source of heat loss for a pool even on a hot day in full sun.
 

atttech-2

Bronze Supporter
TFP Guide
Jul 24, 2015
1,185
Central Valley CA
I have settled on leaving it on as well, like camueller I leave it on while at work uncover for a couple hours while we swim and off a good part of the day during the weekend so I can jump in on a whim. As many have said there are times under the right humidity sun exposure and wind conditions that off might be slightly better but there are just too many variables to manage to be "Trouble Free" I am neurotic enough with out having to worry about a breeze kicking up. Leaving it on reduces heat loss mostly from evaporation and that is good enough to maintain temp and get a decent gain day over day. Testing is almost impossible because weather conditions change from day to day but I would be surprised if on the perfect day for the cover to be off you saw a 1 degree improvement over if it were left on.
 

cdogstu99

Well-known member
Oct 7, 2014
77
Braintree, MA
My experience with the solar cover is as follows:

In my pool, the cover must be kept on for at least 2 days before the temperature of the water increases by about 5 degrees, which is all I need. Any longer than this, and my PH drops pretty quickly below the norm. Some people have reported that they have had issues with algae, but this could be due to circulation issues. With my pool, I do not as the rotating heads help a lot. In addition, suction from the skimmers is slows down a lot.

And yes, the chlorine consumption is cut down to about 1/3 to 1/2 of the normal usage and there is less evaporation with the cover on. I have also had very good success with putting the cover on at night and removing a few hours before swimming activity during the day, allowing the sun to beat down on the water.

My cover was cut in 1/2 + the steps. Then I took a 1" schedule 40 pvc, glued them together to about the with of the pool and rolling the cover off is a breeze. Easy to pick up and tuck away somewhere. You have to figure out what works for your cover and pool.
Any pics of how you put together this cover contraption? Sounds intriguing and looking for a good solution!
 

Catanzaro

Platinum Supporter
TFP Guide
Jul 30, 2014
3,376
Monmouth County, New Jersey
Any pics of how you put together this cover contraption? Sounds intriguing and looking for a good solution!
It is simple. You go out and purchase 10' of 1" PVC piping. I cut the cover down the middle and then all you have to do is pull the cover out of the pool on the concrete. Place PVC on end and start rolling. The difficulty is that you have to get up and pull both sides and then roll again, & repeat. It really helps with 2 other kids on the sides, but you know how lazy this generation has become.

This year, I am thinking of cutting the cover down into 4 pieces. It really does not matter if a little bit of water is exposed as the key is heat retention. I believe this post was done just prior to the heat pump. The cover and heat pump raise the temperature by 1* per hour. Without .5 degree per hour due to evaporation.
 

Vanika34

Member
May 20, 2019
11
Kensington, MD
First month the outdoor temperatures were nice, we had the pool cover on all time except when in use for a few hours a day. Now that we are hitting 90+ during the day, I have found that if I keep the cover on during the day, the water will get very warm but algae will start appearing. Is it fair to state, keep cover off during the day during hot humid summer (Washington DC area)
 

syntax53

Silver Supporter
Apr 12, 2016
77
Philadelphia, PA
I think it all depends on your current water temp. For me, I try to keep the water temp around 84-86. If it's 84 or less at night, or close to that and I know the ambient temperature is going down a lot that night, then I put the cover on to try and save the temperature from dropping too much. If it's 86 or higher I leave it off. I don't think you want to let the water get above 90. Not only is it not refreshing anymore (again, matter of opinion) but that's when you'll start running in to problems.

Also, it's worth noting that keeping the cover on for extended periods of time saves chlorine but also drops your pH and alkalinity levels. There is research/thoughts/opinions on the matter and it revolves around the cover trapping gases that would normally be released into the atmosphere. I can confirm that it's definitely true. And by extended periods, we're talking 3 days+ at a time.
 

Newdude

Well-known member
Jun 16, 2019
977
NY
I put a thin clear plastic sheet (painters drop cloth type) over the pool and it seems to heat up much faster that way.
I had the clear-ish solar cover. Specifically for that reason. The blue ones kind of blend in and look pool-ish. The clear one stuck out like a sore thumb and was hideous but the supposed science to it let the sunlight through to heat the water and then retained said heat at night. It worked. No question it worked. My friends blue ones would be warm to the touch and mine was usually borderlining on hot. We easily got 7-10 degrees warmer depending on how sunny it was early/late in the season. I had the thick one so it was a bit of a chore to use. I may get another one someday but for now we prefer the aesthetics and ease of running down to swim without the cover.
 

syntax53

Silver Supporter
Apr 12, 2016
77
Philadelphia, PA
Wait,
Solar covers cause your PH to drop?
Well, upon further re-reading into what I read before, the cover doesn't directly lower pH, but it prevent the normal rise of pH caused by co2 out-gassing. Basically the natural out-gassing of co2 causes pH to rise. With the cover on it drastically slows that down. If there are other factors in the pool that cause the pH to drop, with the natural rise no longer happening it will take over. You can read stuff in these links:

In my pool, I am always fighting with pH at the beginning of the season while I keep the cover on full-time trying to bring up the temperatures. I am constantly adding soda ash every 3-7 days when it drops down to 7. Now that we are in the warmer whether I have the opposite problem but not nearly as often. My pH steadily rises but it's very slow and I've only had to use acid once to bring it down. Same phenomenon every season.