closing, algae, and chlorine use rate

[bobjdan]

I made it through the summer with no algae problems with my new liner, but on returning from a 9 day trip on 10/17 thought I saw one fairly bright patch of yellow about the size of a saucer by the steps. It looked too bright to me for mustard algae and since we have a lot of yellow flowers near the pool thought it might be from them so I brushed and vacuumed the pool. Before I left in the morning of the trip the chlorine level was 4ppm (I maintained my pool at 4-6 PPM all summer) and I added 1 jug of the 121 oz. 8.25% concentrated chlorine bleach which normally raises the level 4 ppm (25000 gallons in ground cya 60 (as of today but around 55 most of the time), ph 7.5, TA 100). I also stacked 7 of the 3" chlorine tablets in the skimmer.

When I returned home the chlorine level was > 10 (I can't remember the level exactly) and by today it is still 7 ppm. Last weekend I saw a few small disjointed patches (< size of a saucer) that looks like it may be green algae and there was about an 18/6/6 rectangle on the wall of the pool by the steps. A day or two ago I saw the few spots again on the bottom. I didn't address the problem previously because I wasn't sure what it was and it didn't seem to be growing much and I just didn't have enough consecutive time to go into shock mode. I have the following question.

I'm familiar with the algae shocking procedure but what I'm confused about is closing the pool under these conditions. Currently my water temperature is 65 and I know that slows down algae growth but also slows down the chlorine use rate. I recall reading awhile back that before closing, the pool should be shocked and let the chlorine return to normal levels before covering. For the last 4 days my chlorine level has dropped by <= 1 ppm and my CC is 0 and the water is clear as a bell. However, since I've been home it's been cloudy more days than not which probably slows the use rate. So I think that may make it hard to use the overnight drop test as well as to see of there is any chlorine use the same day I shock it. So does that means I'm going to have to strictly go by a visual test which may take days?

Since it takes so long for the chlorine to drop I want to use the minimum amount of chlorine. Pool school says with a CYA of 60 it requires a level of 26 ppm but the pool calculator says 18 with 34 for mustard. If I do 26 it may be Christmas before I get back to normal shock levels. There is little danger of pipes freezing by then but I'd like to get it done before all the leaves fall in and they are just starting to fall.

I know that last year that I shocked the pool to about 18 (no algae) and covered the pool the next day and when I took the cover off, the underside of the cover was bleached white and the remaining part of the liner that wasn't bleached was now bleached. I wasn't concerned because I knew I was replacing the liner in the spring.

Does anyone know the upper limit of chlorine that will prevent bleaching in a covered pool?

So on the one hand I don't want to bleach out my new liner and suffer death at the hands of my wife but I also don't want to open it up with an algae bloom which has happened to me before. Currently my plan is to shock it to 18 tomorrow, check the overnight drop test and let it drop to about 5-6 and cover it when the temperature drops to 60, checking for visible sgns of algae. If algae reappears, I'm not sure what I will do. I'm fairly sure that I want to uncover it when the temperature is below 60, correct? Any suggestions on the best course of action?

Thanks for your help.

 

[duraleigh]

I know that last year that I shocked the pool to about 18 (no algae) and covered the pool the next day and when I took the cover off, the underside of the cover was bleached white and the remaining part of the liner that wasn't bleached was now bleached.

An FC value appropriate to your CYA value will not bleach your liner. Don't know what happened.

Our suggestion is to bring the FC up to SLAM using PoolMath (above under TFP) and cover the pool.

With a CYA of 55, that's about 22 ppm.

 

[bobjdan]

Thanks for the recommendation, scary though it is with a new liner. What is the downside of waiting until it gets cooler and the level had dropped 5-10, ppm, possibly in a week or 2, before I covered it? Is it the possibility that the SLAM won't kill it (although with the little bit visible I would think it should) and the sun will make it grow again?

Since it is a new liner I'd feel safer if I shocked the pool now (I'm not doubting your wisdom but sometimes there are statistical outliers in everything) and waited and watched for a few weeks. I can handle the leaves since there aren't as many since the tornado 2 years ago and they all end up in the deep end and the visible algae is in the shallow end. I could cover it then and if there is any visible algae before then I could raise it back to SLAM levels and then cover it and hope for the best.

I'm leery mainly because my wife has always accused me of bleaching out the liner, not that she knows anything about TFP. It was 12 years old and before I covered it last year there was still some color in the top foot or so near the top and even that was mostly gone. I'll have to admit that I think fixing the problem I had here milky-light-green-water-after-storm-t37213.html?hilit=bobjdan did lead to some bleaching.

Thanks again.

 

[bobjdan]

Ok, I'm worried now. Before shocking, my chlorine level had not changed from 6.5 ppm on Friday a.m. to 6.5 pm on Saturday a. m. so on Saturday a. m. I added 4 jugs of 128 oz. 8.5% bleach which should have raised it to 24. Starting to run low on chemicals I didn't check to see the actual level an hour after the shock. I saw no visible algae and a few hours later I brushed the pool. Since the chlorine level hadn't changed in a day and only .5 in 2 days I didn't check the level until Sunday morning and forgot to check it before it got sun. At 10:30 a.m.. It read 18.5 so I added a jug of the bleach. At 4:30PM with no sun it read 18 which surprised me. I did nothing and at 7:30 a.m. this morning it had only dropped to 17.5 which seemed to meet the overnight drop test. However, this a. m. I also saw a few more small spots near the steps and one of them looks like it may be mustard algae. I'm very confused at this point since the logical conclusion is that adding chlorine seems to make algae grow!

I'm very reluctant at this point to fight mustard algae with the slow chlorine burnoff rate at current temperatures, now down to 62. At this point I'm thinking of committing the TFP sin of adding copper algaecide as a possible solution. I have read many of the caveats about using copper algaecide about staining liners, but personally before using the TFP methnod I had used it many times with no problems other than my daughters blond hair with some green tints that didn't really last that long. It always worked with one bottle compared to using mustard buster and other treatment methods recommended by the pool store even when it was really bad. I seemed to remember an article at TFP advising that it was safer to use copper algaecide if the PH was lowered to, I think it was 7, but I can't find it. Is that true and if not, what is the safest way to use it?

So at this point I seem to have 3 options.

1. Treat for mustard algae (current level I need according to Pool Math is 34 but since without algae the burnoff rate will be very low at the cool temperatures. Is that a safe level to cover the pool with my new liner? Sounds scary to me.
2. Cover and forget it until spring. Will it grow much during the winter covered?
3. Treat with copper algaecide and if so what it the safest method to use.

Any help really appreciated.
Thanks.

 

[chem geek]

If you were following the SLAM procedure including brushing, then are the small spots stuck to the vinyl surface and unable to be brushed away? Do you have any water circulation in the area of the spots? Can you collect any of the material from the spots and is it slimy or squishy or gritty?

If you want to close without a shock level of chlorine, then you can use Polyquat per the instructions in this post.

 

[duraleigh]

You seem to have been satisfied with the management that you did to your pool water in the past and have a basic mistrust or misunderstanding of what we teach.

the logical conclusion is that adding chlorine seems to make algae grow

I suggest you read "The ABC's of Pool Water Chemistry" up in Pool School to get a better grip on chlorine's function.

If what you did before was working well for you, why would you want to change? If you do not have confidence in the principles on the forum then I would not follow them.

You should manage your pool in whatever fashion serves you best and what you have confidence in.

I seemed to remember an article at TFP advising that it was safer to use copper algaecide if the PH was lowered

We don't think it's good practice to EVER use copper in your pool of any type so I really hope you did not see it on this forum.

 

[bobjdan]

Thanks for the response. I did follow the SLAM procedure and there was no problem brushing up the spots, just an easy push. I did not vacuum since I saw little or nothing to vacuum. The water circulation in the pool is good but you bring up an interesting point. The spot, only about 1.5 x 5 inches that looked yellow today was within a foot of the side wall and within a foot of the return line fitting in the shallow end, i.e. if the return line is at 12 o'clock the spot was about 1 foot away in a counter clockwise direction. The eyeball is oriented down and toward the sidewall in a clockwise direction. The spot was also about halfway between the side of the steps and the return line so it is probably in the deadest water in the pool. The other spot I've seen consistently is a few inches in front of the step in the middle of the pool but doesn't really look yellow.

The only other things I can see in the pool besides a few leaves and a small amount of what looks like normal dirt in the liner seems. I also see a few pencil sized squiggles in the deeper parts of the pool but they look dark like dirt. I just checked and I lost 2.5 ppm of chlorine from this morning which was a bright sunny day around 70. I do need to clarify about the water temperature. I just looked closer at the thermometer that I keep in the deep end skimmer and it read 64 but remembered that it reads about 4 degrees low. The reason I know that is I got into arguments with my wife this summer about water temperature when I'm running the new pool heater. She looked at that thermometer and thought it was too cold (85 degrees) so I measured it with my $100 Thermopen instant read thermometer that I use for cooking (and worth every penny of it) and it read 67.7 degrees higher just like it did then. Towards the end of this week though it's dropping into the thirties with a high around 50 so it should drop fairly fast.

So it's looking like the best option may be to get some Polyquat, shock it up a bit, cover it this weekend and see what it looks like in the spring. Does that make sense or do I need to wait until that water temperature a bit closer to 60?

Thanks again.

 

[chem geek]

The longer you wait for the lowest temperature possible the better off you will be as the chlorine and Polyquat will last longer and algae would grow more slowly as well. Then you would open in the spring before the water warmed up too much.

Just note in the instructions for closing that you shock first, then let the chlorine drop, then add Polyquat. The chlorine and Polyquat react with each other and do so faster when at higher concentrations (e.g. shock level). Fortunately, the Polyquat is still effective even when broken up by the chlorine. So why don't you let the chlorine come down to an FC to around 10 ppm and if the water is cooler by then you can add the Polyquat and close.

 

[bobjdan]

Sounds like a plan.

Thanks for all your help.