Backwashing and shocking

Good morning everyone,

My baseline filter pressure is 12 psi. I uncovered the pool June 1 and here it is June 22 and the psi has not changed. The pool stays very clean; the few leaves I've gotten I've fished out with my leaf net. Most debris involves bugs and silt coming down from the trees, and of course it gets filtered with my 1 hp Superpump (sand filter, 20,000 gal in ground). I get a small blob of debris in the bottom of the deep end occasionally and it just takes a minute to hook up my vac hose and take care of it. Of course I brush the pool every week.

If we get no crazy tropical storms this season and my psi stays this low all summer, then theoretically I should not need to backwash at all (I know that dirtier sand cleans better and over-backwashing is hard on the system)? And, if this remains the case, should I backwash anyway when I cover pool in September? Although there will be 8-9 months downtime, I will run pump anywhere from 10-15 times in the overnight hours when temps drop below 28 overnight during the winter months so the pump will not be totally inactive during that time (I live in the south).

* * * * *

With a CYA of 50, when I opened to a crystal clear pool after 9 months down time, I shocked to 15 ppm. Since then I continue to find no combined chlorine. Since I lose about 2.5 ppm a day under full sun I bring the ppm up to 4.5-5.0 each night (with household bleach). So the 24-hour range is 5.0 ppm to 2.5 ppm. I am the only swimmer in the pool most of the time, swimming several times a day, but I think this qualifies for a low bathing load.

Conventional pool advice, we know, tells us to shock every 10 days or so (no matter what), but if I have no CC, and crystal clear water, I shouldn't worry about shocking until I have CC (or signs of algae)? My water is completely odorless and in fact even after swimming there is no trace of chlorine smell on my skin.

One more question: if I get .5 ppm CC should I shock, or wait until I get 1.0 ppm? I apologize that I haven't the time here at work to search the archives. Thank you!

Hi Elsie!

Welcome back--I remember you from "before"....glad to see you've come back to the forum.

Second question first, if your pool is clear, showing no signs of a problem, and not using any chlorine overnight, and you're diligent about keeping your chlorine up adequately, then you could certainly wait until you get 1 ppm CC before shocking--I don't remember where you live, but in many cases the sun will take care of a 0.5 CC before dusk sets in. Almost all pools will have 0.5 at some time, mine almost always does for an hour or so after the kids get out (sweat, sunscreen, dirt off the toys, etc) but it's usually gone by dark. You mentioned tropical storms--I do ALWAYS shock my pool after a hurricane has blown through, though, or after a several-day rain event, even if the numbers are good, because you just never know what the rain will drop into your pool.

As far as your filtering goes, if your pool is very clean, I wouldn't expect your pressure to rise, and I see no need in backwashing it until the pressure does rise. I would, however, backwash it before closing--you don't want all the "gunk" in there from a whole season having all that time to grow bacteria and other stuff that you'll have to kill off when you reopen.

Janet

Hi Janet,

All excellent advice, thank you so very much! I'm in central Alabama (a transplant 8 years ago after 47 years in my native Minnesota). As I recall you're in Louisiana and keep a CYA of 100 because of the nonstop hours of full sun on your pool...funny what things stick in our minds (assuming my memory is serving me correctly). Of course these days the mention of LA--at least coastal LA--conjures up very sad thoughts. Tragic beyond words.

Thanks again for confirming my thoughts on the backwashing and shocking! And I'll "see" you around the forum!

Quote:

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Originally Posted by elsie

As I recall you're in Louisiana and keep a CYA of 100 because of the nonstop hours of full sun on your pool...funny what things stick in our minds (assuming my memory is serving me correctly).

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Yup, that's me! Still down here, oil slick or not :p

Janet

Hi everyone! I'm new to The PoolForum so if my post is out of place, please feel free to move it.

We are having an issue with backwashing and shocking our pool it that we have done it more to our new pool installed four months ago, than we ever did with our old above ground pool. It involves an algae issue but after reading the posts in the algae forum, I decided to post here because in the last 15 years we've had above ground pools, we have primarily use a shock product - and an occasional clarifier product... and never checked any water levels! I vacuumed the pool every other day and my husband backwashed every other week or so. We never had any problems like this before.

I am vacuuming the pool AT LEAST once a day, in the morning, and before the sun sets, the bottom of the pool is covered with a fine green/brown dusting as described in the algae forum. And I have to backwash AT LEAST TWICE before I finish vacuuming!

We will try the DE and filter sock (if I can find one) and I will attempt to find a water tester so I can provide you with the levels. Meanwhile, I need to find some kind of primer on pool maintenance and what all the abbreviations mean and how to deal with each.

Meanwhile, can you tell me if I'm destroying our filter by backwashing so much? (The Doughboy documents are very sparse)

Thanks for your time!

Hi, Judi,
Welcome to the forum!!

For right now, backwashing your filter frequently is much better for it than letting the pressure get too high and overloading your pump. It shouldn't hurt the filter; however, if you're having to backwash that often, there are obviously problems with the water that you need to address.

Does your filter have a vacuum to waste mode? That would allow you to still vacuum but to bypass the filter so the frequent backwashings wouldn't be necessary.


By "occasionally using a shock product and a clarifier product and not testing any water levels", you may have created a pool that's going to take some time and patience to fix, but I'm sure we can help you with it.

If you'll have the water tested with a drop-based kit (no strips!) and post numbers for at least two of the three: Free Chlorine, Total Chlorine, Combined Chlorine in addition to pH, Total Alkalinity, CYA (stabilizer), and Hardness, I'm sure we can help you get the algae problem fixed so that you don't have to spend nearly as much time vacuuming.

We also need the ingredients of the chems you've been using in the pool (specific ingredients, not just "shock").

Also, you really need to get a good, drop-based kit so you can do your testing at home and make sure that your readings are accurate. In order to clear up an algae problem, this is going to be key. We recommend the Taylor 2006K, which can be found online. Leslie's also has a relabeled version of that kit on their online site.

In the meantime, read through the "stickies" at the top of the forums--most of the general water chemistry basics and methods are in those stickies. You can also check out our sister site PoolSolutions.com and there's LOTS of information there that will help you understand what's going on with your pool. And, of course, we're here to help!! It will be helpful if you'll just keep all the information regarding this situation in this one thread, so that all the people trying to assist you have all the info in one place.

Janet

OK Janet, got a test kit from Leslie Pools today... here goes:

FC = 2
TC = 3
CC = 1
PH = 7.5
TA = 150
CYA = 70

The pool looked great yesterday. I wasn't able to vacuum this morning and took the readings this afternoon when I got home. Pool's green on the sides and around the base. Now it's raining like mad... we're getting rain bands from the hurricane...

I don't have the filter sock or DE yet.

Thanks again for your time.

Judi

Hi Judi,
Not Janet here, but hope I'll do!

With a cya of 70, your chlorine levels are not near high enough to keep algae from forming much less to fight it!

Stabilizer . . . . . . Min. FC . . . . Max FC . . . 'Shock' FC
=> 0 ppm . . . . . . . 1 ppm . . . . . 3 ppm . . . . 10 ppm
=> 10 - 20 ppm . . . . 2 ppm . . . . . 5 ppm . . . . 12 ppm
=> 30 - 50 ppm . . . . 3 ppm . . . . . 6 ppm . . . . 15 ppm
=> 60 - 90 ppm . . . . 5 ppm . . . . . 10 ppm . . .. 20 ppm
=> 100 - 200 ppm . . . 8 ppm . . . . . 15 ppm . . .. 25 ppm

As you can see in the chart above, you need to keep your cl between 5-10 ALL the time and when you need to shock, you'll need to take it up to 20ppm. Since you are reporting a CC reading of 1, and you have low FC level and you are seeing algae, all these things tell you that you need to shock the pool and try and hold the cl at 20. The more times per day that you can test and add bleach to get your cl back up to 20 the better. The very minimum is twice per day: early morning and in the evening when the sun is off the pool. But, if you can test 3 or 4 times per day it will clear up faster. The key is to sustain the high cl reading and not let the FC yo-yo up and down. When you get to the point where you are not losing more than 1ppm of cl from sundown to sunup and when you have a CC reading of 0 and no more algae, then you can let your cl drift back down to between 5-10. Never below 5 however or you will fight algae again. Also run your pump 24/7 while you are trying to clear this up. Also, brush the sides and bottom of your pool daily.

What exactly have you added to this pool -- meaning ingredients, not just "shock"? Your cya is already high at 70 so you really shouldn't use any trichlor pucks or dichlor powder in your pool. Best to stick with bleach or liquid chlorine.

What is the volume of your pool?

Thanks Watermom!
Our pool holds 8000 gals. We have always exclusively used a product called Shock PLUS (by aqua chem). They are 1 pound packets that treat 12,000 gals. I don't know why we started using an entire packet per treatment, but we did. Like I said before, our problems started three months ago with our new pool. The active ingredient is sodium dichloro-s-triazinetrione (58.2 %). The remaining 41.8% is "other ingredients". The package instructs to use once a week to create sparkling water, reduce chlorine odor and eye irritation, and does not increase pH.

I can work on the pool in the morning and evening, but for the rest of the day, this being Texas, the sun is unmerciful. Could it be the sun? We lost a shade tree and one of our pool umbrellas so we have many more hours of direct sun on the pool this year. In any event, I will start the bleach regime and let you know.
Judi

In your pool, each quart of 6% bleach will raise your cl level by just about 2ppm. Also, with a cya level of 70, you shouldn't use any more dichlor (shock plus packets) as they are stabilized (which means they have cya in them) and you don't want your cya any higher.

Keep us posted!