Algae prevention with a solar cover

[Catanzaro]

Last year, and prior year, I had no heat pump and used the solar cover from time to time, even leaving on for several days (3-5) without removing, allowing to breathe, etc. with no algae what so ever. Now, let's skip ahead. At the end of the season, a SWG, and heater was installed and used cover for a little bit and then the pool was closed. Never any algae or issues.

Move forward to 2018 and only last week, did I start visually seeing spots of algae pop off along the bottom of the deep end only and in other small spots. Brushed away easily. So, I quickly brushed, removed cover for one day and within hours pool was back to normal. Registering no CC's and overnight test no problem. The water is at 85* and the surface water with the thermometer is registering about 4*-5* more (first 6" inches of surface water). Can only imagine right underneath the cover is way more during the day with the sun beating down.

A few days later, same recurring issue and I increased the chlorine to 10% of the CYA and even with a dose of Poly-Quat 60 (Of course I do not use and only for closing, but what the heck), still the same issue. I know that there have been a lot of threads on the forum about this and it is hit or miss with pool owners.

A few questions:

1) I know that it is possible that the cover is contaminated? How do I clean the bottom (bubbles) and top side? I have been rinsing with fresh water to remove the dried salt each day.

Even if the cover was peeled back to a few hours, this did not help.

2) Because the cover is cut to fit the pool and covers 99% of the surface area, would it be better to trim 1' all the way around and even in the middle where it is cut in half? This will allow the skimmers to pick up the surrounding water as well without restriction flows.

I have very good circulation and water moves very fast. In addition, the rotating heads "The circulators" mixes water very well and the fusion eye balls pull water off the surface and bring down, which increased power. I can not imagine that chlorine was not reaching the areas in question. And I know that a lot of things happen when a pool does not breathe. So my thoughts are only to place the cover on at night and remove about 9 a.m. in the morning. There is a lot of latent heat lost in the a.m. on the surface, but the overnight night drop is not that bad overall. I figured that the cover would now be even easier to remove than before. The best thing to do right now is probably clean the cover in the driveway with a little bit of bleach, light scrubbing and a quick rinse after a few minutes, etc.

 

[Teald024]

Your cover is not causing your algae issues. I leave my cover on the pool just about every minute the pool is not in active use. I've never had a problem. I'm failing to understand why the properly chlorinated pool water is any less effective at preventing algae on the cover than it would be at preventing algae in the water or on the walls. Even if the cover is contaminated, that is exactly what the chlorine is used for, killing the greenies in the water. I've never cleaned my cover directly. The bottom is always in contact with chlorinated water. The top gets dirt, pollen, rained on, etc. When I roll up the cover on the reel, both sides (top & bottom) get submerged in chlorinated water.
Is it possible that what you are seeing is lower usage of the pool and water not being mixed properly when the cover is used more frequently? The warmer water is making the algae reproduce faster.

 

[Catanzaro]

Your cover is not causing your algae issues.

Yes, my cover is causing algae issues, whether or not contaminated is a different story. I actually removed the cover, dove down with goggles and looked very closely. Removed the algae with a microfiber towel as it is easier than trying to use a brush underwater. Have not had a spot of algae since joining TFP. Cover off last night and this morning the pool is crystal clear without any formation of algae.

Is it possible that what you are seeing is lower usage of the pool and water not being mixed properly when the cover is used more frequently?

The pool has circulators. Whether I use 4 or 6, it makes no difference. This event has been happening for about 2 weeks. Yesterday, I cleaned the cover with bleach (both sides) in the driveway, etc. Although, there is water flow at the surface and the temperature disparity between pool and surface (where thermometer is placed varies about 4*-5*). Right underneath the cover, I will bet you we are talking 10*-15* difference, but only an inch. There have been many reported cases on the forum about covers and algae (It is hit or miss). Never happened until the heater came into play. My levels are perfect.

What I did yesterday is also cut another 6" all the way around so the pool can breathe a little better and the skimmers can pick up surrounding water. The spots of algae were very small and only in the deep end, down about 8' feet and in the corners. There were some small minor areas as well, but very limited. I will only place the cover on the pool at night (at 8 p.m., the earliest and take off before 9 a.m.) in the morning. If I have to leave, then around 6 a.m. Only need to retain overnight heat as the pool stays pretty warm and the heat pump is extremely efficient. I will spend the extra $3 per day to maintain the correct temperature. Also, during the day, the pool generated 2 extra degrees, and wound up from 85* to 81* with an overnight drop. With the cover, I would loose no more than 2*, and this is what I am trying to prevent.

The warmer water is making the algae reproduce faster.

Probably. Here, we are constantly learning and that is what makes this community a great place to be. I figured not having the cover on during peak sun hours during the day will do the trick. Plan on trimming another 6" off the cover as still a little heavy, even though cut in half. A real PIA to remove and store. To put on the pool takes 3 minutes because the cover is wrapped up in a 1", 15 foot PVC with end caps.

Thanks for your advice & speak to you soon.

 

[Teald024]

Yes, my cover is causing algae issues, whether or not contaminated is a different story. I actually removed the cover, dove down with goggles and looked very closely. Removed the algae with a microfiber towel as it is easier than trying to use a brush underwater. Have not had a spot of algae since joining TFP. Cover off last night and this morning the pool is crystal clear without any formation of algae.



The pool has circulators. Whether I use 4 or 6, it makes no difference. This event has been happening for about 2 weeks. Yesterday, I cleaned the cover with bleach (both sides) in the driveway, etc. Although, there is water flow at the surface and the temperature disparity between pool and surface (where thermometer is placed varies about 4*-5*). Right underneath the cover, I will bet you we are talking 10*-15* difference, but only an inch. There have been many reported cases on the forum about covers and algae (It is hit or miss). Never happened until the heater came into play. My levels are perfect.

What I did yesterday is also cut another 6" all the way around so the pool can breathe a little better and the skimmers can pick up surrounding water. The spots of algae were very small and only in the deep end, down about 8' feet and in the corners. There were some small minor areas as well, but very limited. I will only place the cover on the pool at night (at 8 p.m., the earliest and take off before 9 a.m.) in the morning. If I have to leave, then around 6 a.m.

Please elaborate on how a cover causes algae.
Just because the algae did not show up the one night you took your cover off doesn’t mean that there’s not algae in the water.
Algae growth is a function of correct chlorine levels and proper circulation to get the chlorine to all the places it needs to be. It’s as simple as that.
Even if your cover was infested with algae, proper chlorine in the water should neutralize it without infecting the whole pool with an algae outbreak. Granted yours algae spots are only in a couple of corners but it’s still not the covers fault.
A proper SLAM process should be running to make sure you kill all the algae.

 

[Catanzaro]

Dave:

If you search the forum on this issue, you will see that this is a reported problem amongst many pool owners. Getting down to the scientific reason behind this is way beyond my knowledge. As previously stated, my algae spots were just starting and so small, that there is no need to SLAM the pool. My water is crystal clear, and registering no CC's. If you go through all the posts and other information you will see that this happens with a cover (Why, I am stumped, but there are underlying reasons behind this). Probably is that some pools need more breathing room. A total of 2 days later and absolutely no algae in my pool, and I keep my levels lower than the recommended because of the circulation in my pool.


solar pool covers and algae site:Pool School - TFP Home Page

 

[Teald024]

If you search the forum on this issue, you will see that this is a reported problem amongst many pool owners. Getting down to the scientific reason behind this is way beyond my knowledge.

I did do some searching and didn't come up with anywhere or anyone who could really point to why this happens. And in science, that isn't proof that the cover causes the algae. It may be a factor, but not the root cause. I'm not convinced.

As previously stated, my algae spots were just starting and so small, that there is no need to SLAM the pool. My water is crystal clear, and registering no CC's.

Umm, having algae is EXACTLY the reason to SLAM. tiny spots or a swamp are not part of the decision tree. And wiping it off with a towel is not the TFP way to remove algae.
I've had one time where the water was crystal clear, passed OCLT and no CC's, 12% FC:CYA ratio and yet I had one spot ~2" x 1" of algae. The pool hadn't been used or brushed for 2 weeks prior to that point. Low circulation and local low chlorine was the issue.

If you go through all the posts and other information you will see that this happens with a cover (Why, I am stumped, but there are underlying reasons behind this). Probably is that some pools need more breathing room.

This doesn't happen with a cover. It happens to some people who use a cover. There's a difference.
Breathing room?? That sounds like pool store hogwash... Which part of the chemistry requires breathing room? I'm not a chemist and I would welcome some additional info on this.

A total of 2 days later and absolutely no algae in my pool, and I keep my levels lower than the recommended because of the circulation in my pool.

Lower chlorine levels seems like more of a cause of algae than a cover. I don't believe I've read anywhere that we can drop FC if we feel we have good circulation. And since your algae is showing up in the corners of the deep end, I'd say that is one of the places least likely to have good circulation.


What are your typical test results before the algae showed up? Before you upped FC to 10% of CYA?

 

[Catanzaro]

What are your typical test results before the algae showed up?

Dave:

My CYA is 70 and has dropped from 80 because I have had to dump water because of excessive rain. My FC levels usually wind up at 2 ppm in the morning (early morning) based on my extended testing with the drop test, registering no cc's. My SWG is set to run from 11 a.m. to 7 p.m (8 hours) at 50% with the pump. Based on my calculations, my T9 cell produces 1.25 lbs. of gas in a 24 hour period at 100% level. Pool Math states that at this level, I am producing 9.5 ppm in a 24 hour period at 100%. A total of 8 hours is 1/3rd the time, or 3.167 ppm at 100%. Now, divide that by 2 for a 50% level, and I am at 1.5835.

Last year, I only had the cover on without problems. Although, no heater at all. The water temperature never increased with the cover on, but only retained the heat through evaporation (They are good to have with a heater). No issues last year and I did not use the cover at all after the heater (because it was at the end of the season). This year, with the heater and cover, I would experience this issue and only in the deep end as I stated. The returns (spin) and move water very well and circulation is good. Even 3' down in the deep end I saw some spots.

In summary, without the cover, my levels were kept lower than the minimums (I also suspect my phosphate level is extremely low) and have never tested since joining TFP and do not use any removers either. Not once did I experience algae, any spots, registered any CC's or burned more chlorine than necessary. In fact, the last several years, my avg. was between 1.33 and 1.56 weekly depending on activity. If I have more than a few children or adults in the pool (Like 10-15 people) with lotions, etc., I manually dose the pool to add another 4 ppm early morning to prevent or minimize any issues.

The cover was trimmed by 6" all the way around (cut in half) and yesterday I placed the cover only on the deep end (late at night), like 8 p.m. and removed at 6 a.m. as a test. No traces of any algae whatsoever and my levels were at 2.5 ppm this morning without registering any cc's. What I probably will do this week is trim the cover another 6", giving me 1' of breathing room all the way around the perimeter of the pool and 2' in the center. I truly believe the surface right underneath the cover is at least 10* hotter, but just my gut feeling.

Neither here nor there, I will experiment with the cover. If there is no success, the cover will not be used again. Not worth the aggravation of putting on and off to save the extra $30-$50 per month by reducing the heater use over 4 months. Take care and speak to you soon.

 

[Teald024]

I believe you are seeing compounding issues all add up to small patches of algae. None by themselves is enough to let the algae survive but all together pushes you over the breaking point.


I believe the main issue is FC. Minimum FC with SWG at 70 CYA is 3ppm and at 80 CYA is 4ppm. With lowest FC of 2ppm, you are well below minimum 66% and 50% respectively. Measured in early morning, but SWG doesn't start til 11am. And it's 2ppm where you measured it, not everywhere in the pool.


The water jets do a good job of circulation, but they're not perfect. The chlorine won't be ideally uniform throughout the pool no matter how much you try. Is the pump running 24/7 or just while the SWG is running?


FC and circulation coupled with potentially warmer water with the solar cover is likely allowing algae to grow slightly faster.


Before you cut the cover and go down that rabbit hole, why not just leave the cover on and up your FC so you don't go below min FC values. If you have 6" of space around the pool, then I'm guessing 15-20 sqft of open area. That should be enough to breath.
You won't necessarily run the SWG harder at a higher FC, it'll just start and end at a higher level. Run that experiment and see what you get. It'll be easier than cutting that cover. I think you're focused on a problem/solution that may not really fix the cause of your main issue.

 

[Catanzaro]

I believe the main issue is FC. Minimum FC with SWG at 70 CYA is 3ppm and at 80 CYA is 4ppm. With lowest FC of 2ppm, you are well below minimum 66% and 50% respectively. Measured in early morning, but SWG doesn't start til 11am. And it's 2ppm where you measured it, not everywhere in the pool. The water jets do a good job of circulation, but they're not perfect. The chlorine won't be ideally uniform throughout the pool no matter how much you try. Is the pump running 24/7 or just while the SWG is running?

I fully understand about the minimums here, and there were never any issues with the algae spots prior to the cover. When I test, the pump always runs for at least an hour in the a.m. (As I turn on manually). Pump only runs during the 11 a.m. to 7 p.m. schedule. Cutting the cover is not just about breathing, but more about making the cover a little bit easier to manage (take off and put on). If 85%-90% of the pool surface is covered during the evening, for at least 10 hours, I honestly believe this is sufficient to retain the overnight heat.

My next experiment will be with the cover but more and on both ends over 2 days, when not in use. If there is algae spots, then I will increase to SLAM level for 2 days and do a little bit more of experimentation. Honestly, if these solar covers came without the bubbles, just a think piece of vinyl or plastic (whatever the material is), I would like it better as it would be lighter and easier to clean as well. Thanks!

 

[domct203]

If you keep enough FC in the pool, algae will not grow. Period.

I also use a solar blanket, and it is on the pool every evening, as well as any partly cloudy or windy day (90% of the time basically). I do not get algae in the pool.

I've seen algae start to grow in the popped bubbles, or on top if the water has been stagnant, but neither has ever resulted in algae in the pool.

I also recommend you bump your FC target up a bit. Everybody's pool is different, what works for one is not guaranteed to work precisely the same for another.

 

[Catanzaro]

I will increase my FC up a bit, but I was only visually seeing small algae spots in only a few areas, nothing major. Cutting the cover appears to have allowed the pool to breathe better and the skimmers to work freely. This evening the OCLT will be performed to determine if the loss is more than 1 ppm. Water is crystal clear. Thanks Dom!

 

[Poolzzz]

My CYA is 70 and....I am at 1.5835.

Minimum at 70 is 3 ppm. You are at 1.5835?

Algae aside, are you sure your pool is sanitary at those levels?

 

[Catanzaro]

Minimum at 70 is 3 ppm. You are at 1.5835?Algae aside, are you sure your pool is sanitary at those levels?

The 1.5835 is the calculated amount that the T9 cell produces over a course of one day. My morning levels are around 2.5 ppm to start off with, sometimes slightly higher, and maybe by 11 .am. slightly lower. This is just an average. Saturday, my morning levels for my weekly testing was 5 ppm. Regarding the pool being sanitary, is anyone every sure? With the SWG, I have kept levels a little lower with great success, again only having these minor spot issues with the cover. No cover on for a few days and the spots did not reappear.

 

[Teald024]

I will increase my FC up a bit, but I was only visually seeing small algae spots in only a few areas, nothing major. Cutting the cover appears to have allowed the pool to breathe better and the skimmers to work freely. This evening the OCLT will be performed to determine if the loss is more than 1 ppm. Water is crystal clear. Thanks Dom!

Really?!? Have you been to the PS lately? It sounds like you have come to accept sub-par water as a way of life. IT DOESN'T MATTER WHAT THE oclt SAYS, YOU HAVE (had) VISIBLE ALGAE!

I'll thank Dom as well, not because he added anything new, but because he agreed on what I've been telling you for 3 days. :gone:

 

[Mendy48]

Interesting thread. I've never heard of the solar cover causing algae...I'm convinced it's FC uniform level in the pool. I have a relative who also thought her solar cover caused algae, but it was her low FC range in her pool that caused the algae build-up. I don't, under any circumstances, allow my FC to be close to the minimum requirement of 3ppm. It's always at a neutral level or 1ppm above the maximum level. I leave my solar cover on, when not in use, at all times. I haven't run into this issue of algae based on my solar cover. I think that keeping the right FC range... more than your minimum requirement is key here.

Also, you may need to SLAM. It really depends on your numbers.

 

[Poolzzz]

My FC levels usually wind up at 2 ppm in the morning (early morning) based on my extended testing with the drop test

You said usually 2ppm earlier. With 0.5 drop test resolution it could be 1.5ppm. Just thinking you are well below the minimums defined by TFP which were developed for sanitary reasons as well as algae. Without expertise to "go it alone" it might be wiser to stay comfortably within the guidelines.

Also for another data point, I have a bubble cover on 24/7 taken off only when swimming and immediately put back on. It's 100% area coverage. I follow TFP guidelines and have yet to have algae. I keep my pool between 90-95F so it is hotter than most as well. If you follow TFP guidelines I expect your algae issue will disappear. Although you might have to SLAM first given you have an outbreak of algae otherwise you may be harboring nascent algae growth and not know it.

 

[Catanzaro]

Although you might have to SLAM first given you have an outbreak of algae otherwise you may be harboring nascent algae growth and not know it.

In the works first thing tomorrow morning. Just finished brushing the pool real well, vacuumed floor, and went in with the goggles as a nice day to inspect and everything looks good. I guess that I have become a little more relaxed since the SWG. With the daily additions of bleach, pretty much had it down to a science.

 

[Catanzaro]

I wanted to update this thread. I marked with tape and notes (blue tape) on the concrete, all the areas that were in question over the last few days. Brushed those areas, turned on the filter, and water looks great. Passed the OCLT 2 days in a row, even with higher levels and SLAM conditions. Filter shuts off, next day, same areas in question show same signs, and nothing else all over the pool.

It appears that this has been dirt and pollen all along, which could look like algae because of the reflection of the blue cover, water, etc., making everything look green. Strange part is that the same 4 to 5 areas on liner seam 3' down and deep end corners show the same spots from a distance. I was able to get down with my fingers and nothing is slimy or even creating a puff. While appearing green, it has been pollen and dirt all along as I carefully looked again with goggles. No other areas of the pool were affected. My eyesight is not what it used to be either and this is always first thing in the morning which is even worse after waking up. Live and learn.

Thank you everyone for your help. Enjoy the rest of your summer.

 

[Teald024]

Question? why would dirt and pollen gravitate to the same 4-5 spots and not other areas? Isn't it more likely that it is the same spots because the algae never got fully cleaned and just grew back in the same spots?

If this was any other SLAM, we would say your water isn't clear yet, keep SLAM'in... You haven't passed all 3 criteria yet.

 

[Pool_Medic]

You are missing some keys.

Water can indeed have algae growing in high chlorine, dead spots due to poor circulation. Ever brush a crystal clear pools steps, where the liner is attached? Or a ladder? There is always minute amounts of algae there.

Pools need to breathe to aid in oxidation. Leave a solar blanket on a pool with high chlorine and yes, it will get some algae growth.

Small amounts of visible algae never made me run and slam, in my opinion it’s a matter of brushing those little nasties and getting them in the water where my chlorine can kill it.