Using Bleach in the Pool

I am reading all I can on this site. But, I have an algae problem (just bought a house with a pool) and I have limited time to spend on the board during the work week.

My question is how much liquid, store bought bleach should I use to shock a 25,000 gallon pool? I used shock so far (from pool supply store), twice, and have scrubbed the pool twice, and used algaecide twice, and vacuumed the bottom of the pool (to waste) once. The pool is still not clear, but making progress. I would like to avoid buying loads more of granular shock.

Also, after the pool is winterized, what can I expect, visually, when I remove the cover in the spring? More algae?

How much bleach you'll need will depend on the chlorine level you have to attain to kill the algae, which in turn depends on your CYA level. So...if you could please post a set of test results (drop-based testing, please no strips!), it will help us give you better answers.

As far as removing the cover in the spring, what you will find can range from crystal clear water to dark brown water, depending on how you close, how much debris gets into the pool while removing the cover or during the winter, when you close and open, what your CYA level was at closing,and many other factors. The best thing you can do is get the water balanced, add a dose of polyquat, allow to circulate for a day or so, then shock the pool and cover it. If you wait until the water is as cold as possible to close, and open as soon as you can before the water warms up, then you stand a much better chance of opening to a clear pool. What type of pool is this (liner, plaster, gunite, etc), and what type of filter and size pump do you have?

Welcome to the forum!

It's impossible to tell without good test numbers. You'll need to get chlorine levels (both free--FC and combined-CC), pH, Total Alkalinity (TA), and Stabilizer/CYA. If it's a concrete or other hard material (not vinyl), you'll need Calcium Hardness (CH) as well.

The "Best Guess" table tells you what level of Free Chlorine you need, relative to your stabilizer level. But how much to add? Well there's a formula, but the shortcut is that one gallon of 6% bleach will add about 2.4 ppm of Free Chlorine to your pool. That doesn't mean it will RAISE your FC level that much, at least not for long...algae may break it down. 12% liquid chlorine (sometimes called Liquid Shock) will add double that per gallon, or 4.8ppm.

The best investment you can make is the $50 to $70 for a Taylor FAS-DPD full test kit, the K-2006 or K-2006C. It's not on my sig right now but is on Pooldoc's and on some of the other mods. The kit will pay for itself hundreds of times over and all the test chems ("reagents") are replaceable.

In order to follow the link for the test kits, you'll have to log out, go to the main forum page, and then find any post made by myself, Watermom, or Pooldoc--new subscribers usually can't follow the links from here while logged in until Ben has completed the registration process.


Janet

As of last night the PH is at 7.6, Chlorine 3.0, the CYA test I was not able to administer, because the test kit I inherited is missing that componnet right now. I used the test strip, which agreed with the test kit #s, and gave me a "very high" stabilizer reading or 150.

I am told the pool is 25,000 gallons, the filter is a Hayward sand filter S220T, with a Hayward super pump 1.0 HP.

Pool is cloudy. Seems to have lots of dead algae in it, which moves/billows up when touched and is no longer clingning to the walls or floor. I suppose I will have to vacuum to waste again tomorrow and see what happens.

If you see the filter pressure rising, then the filter is doing its job in filtering out the dead algae. Remember, chlorine kills it, then the filter (or vac'ing to waste) removes it. However, you won't know if you've killed it all off until you can test chlorine after the sun is off the pool, and the next morning before the sun is on the pool, and lose less than 1 ppm of chlorine in the process. However, to do that, you are going to need drop-based testing--strips simply are not accurate or reliable enough to use for this purpose. Also, strips do a very, very poor job of measuring CYA--they can usually tell you if there is, or is not, CYA in the pool, but you need an accurate CYA level before I can begin to tell you where your chlorine level needs to be for shocking purposes,. The Best Guess table that Carl referenced above will explain that more fully, but in order to access it you need to log out to the main forum page, to go the "Using chlorine and chlorinating chemicals" subforum, then open the second sticky for the Best Guess Chart.

I have drops and use them for the chlorine, ph, etc. But not CYA, because the test kit is missing a piece. Also, it is probably not the best kit (pool time), and it is probably old. I will replace on Monday. In the mean time, I will test again tonight, which will be 24 hrs after last test. I am grateful for your help. Thank you.

I will also test in the morning, and compare to the evening test. Thank you.

If you don't lose any chlorine, then you just need to filter out the dead algae. However, if your guesstimate of a CYA at 150 is anywhere close to accurate, it won't be long before you do have algae growing--in a pool with CYA over 100, you need to be keeping your chlorine at a minimum of 8 ppm--normal operating range for you would be 8-15 ppm, with a shock level of 25 ppm. In a 25K gallon pool, each half-gallon of 6% bleach will raise your chlorine level by 1.2 ppm, just to give you an idea....if your chlorine is now at 3 ppm, then to get to 8 ppm you would need to add 2.1 gallons of 6% bleach.

That's why your CYA level is so critical--it determines how high you have to keep the chlorine in order to keep the pool clear and clean.

Well, I tested it tonight and the chlorine was down to 2 the ph was down to 7.4 (according to the drops) and the stabilizer on the test strip dropped to the appx 100 reading on the strip. This is 24 hrs after I put 3 gallons of bleach in the pool (6%). For that matter, I put 3 gallons in the night before too. Should I wait to test in the morning to see where I am at or add more bleach just to be safe?

The idea behind testing to see if you have a chlorine demand is that chlorine is consumed by two things: sunlight and pool goo. You can't really judge by looking at a 24 hour chlorine consumption whether you still have algae, because you don't know how much of the chlorine was consumed by the sun and how much by the goo. That's why you need to test at sundown after the sun is off the pool and again in the morning before the sun hits the pool if you're trying to establish whether your algae is all dead. You are always going to lose some chlorine during the day, due to the sun.

With a CYA at 100, you still need to keep your chlorine at a minimum of 8 ppm, otherwise you're inviting algae to start. You'll need to look at your results taken at night and in the morning to determine whether you still have an algae problem or just dead algae that needs to be filtered out.

If your chlorine is at 2, you need to add more bleach to get up to at least 8 ppm--but if you determine that you still have overnight chlorine consumption, then you need to shock it up to 25 ppm.

Maybe Janet has already mentioned this to you in your thread and I just missed it when I scanned through it but you need to buy a good kit. Especially if your CYA is over 100 like you think it is, you'll have to run higher chlorine levels than the kits you'll be able to buy locally will be able to test. You need to buy the Taylor K-2006 or 2006C kit which you can find in Janet's (Aylad) signature block in post #2 above. It can register chlorine levels up to around 50ppm I think as opposed to around 5 like most kits.

Tested tonight (had to go away for the w/e). It was 2 for chlorine. 7.4 for ph and the CYA was over a hundred. I had to use an old tube for the CYA test and the reading #s only went up to 100. I am guessing it was over 120 based on the spacing of the lines, but it is a guess. I will test again in the morning.

I have 9 gallons of 6% bleach waiting to go in the pool if necessary and can get more. The pool is slowly, very slowly, clearing (1.5 weeks after initial shock treatments), but is still cloudy, especially in deep end. No new algae has popped up. I can still see dead algae on the bottom.

@ aylad, the test this morning showed chlorine between 1 & 2. LAst night was 2, but the lighting was different, in the room, so maybe that affected the change in the reading? Ph remains at 7.4 and the CYA remains above 100, at approx 120.

Water in the pool remains cloudy.

@Watermon, I am going to buy at Taylor Kit. I tried to find something locally when I came back into town, as a stopgap, but was shut out.

OK. While waiting for my new test kit to arrive (Taylor 2006C) I tested the pool Sunday night, Monday morning and Monday night, Tuesday Morning and Tuesday night. All tests were similar, Chlorine near 2 (+/- .5) , ph at or near 7.4, CYA at 100 - 120 (guess because the tube only goes to 100). The pool is still slowly clearing, but cloudy (for past 2 weeks). I went ahead and put 8.5 gallons of 6% bleach last night, after the last test, tested again this morning, all levels are the same, except the chlorine, which is not measurable beyond 3 on my current drop kit. Clearly, the Cholrine has spiked, as intended. I calculated that I should have added over 20 ppm to the chlorine count, which would leave me short of the suggested 25 (I had no more bleach). If there was any more living algae in there, hopefully it will still be enough. Thats all I have for now.

OK, my Taylor kit arrived. I tested pool last night. It was 6.2 FC, 7.4 ph, 120 ppm TA, 450 hardness, CYA off the charts...well above 100, probably around 150, but that is a guess based on how far below the 100 marker that the warer level was. I added 182 ounces of 6% bleach. This morning the FC was 9, CC was 4, the rest of the readings were the same as last night. Forgot to write down the CC last night, so I have no comparison.

Water remains cloudy and slightly green. Still unable to close the pool and cover it. This has been going on for a month now. Thinking about draining a couple of feet out of the pool and adding water to drop the CYA level. I do not want to have to go through this next season when people are actually swimming in the pool.

25,000 Gallon gunite, Hayward 220ST filter, 1 HP pump.

Update: I have been keeping the Chlorine level high, 10+ FC with an occassional shock. It is still cloudy. But, I can see the bottom of the shallow end and it looks like I can see about 5 ft. down into the deep end. I have been brushing the walls, and I vacuumed over the weekend. Hoepfully, we are close to the end of this mess.

Last night I shocked the pool again. Before I shocked, the pool was 16.5 FC, .5 CC, 7.6 ph, 110 TA, 370 CH, 150 CYA. I added 4 gallons of liquid shock from a pool store (Unstabilized chlorine, 10% or 11% depending on which part of the label you read. Up until now, I have been using store bought chlorine (6% Dollar General)). I have gone through a lot of chlorine and want to try a higher concentrate with less bottles.

After I shocked pool, I tested the FC 2 hrs later. It was 27.5.

This morning I tested. It was 27.5 FC, 0 CC, 7.8 ph. 120 TA, CH 370. So the ph went up, which was odd. But, the other odd thing was when I tested the TA, it turned from green to a pale yellow color, rather than a pinkish red color. I tested it twice, same results. Why did the color change? Also, why did the ph go up?

I am assuming all the algae in my pool is dead and I am waiting for everything to settle, due to the FC and CC. Is there anything else I need to do before I get someone to shut down the pool for the winter?

Thanks for your help.

membership updated . . .

Update: The previous evening I brushed and shocked. The next morning I had no change in FC & CC readings. Last night, for the sake of being throrough and aggressive, I brushed and shocked again, bringing the FC level up to 32. The FC dropped to 28 this morning, and CC was at 1. I suppose this means I still have algae to contend with? I will shock again tonight.

On another note, I spoke to the builders of my pool and they sent me a copy of the original blueprints. It is 16 X 40, 24,811 gallons (I was close in my estimate). Pool is older than I thought....35 years.

Hayward 220ST filter, 1 HP pump.

The pH went up because your chlorine level is so high--chlorine levels above about 15 ppm on the Taylor kit will give falsely high pH levels, so don't adjust your pH any until the chlorine comes back down and you get a reliable reading. I suspect that's the same reason that your TA changed colors the way it did.

If you are still losing 4 ppm of chlorine overnight, then you are indeed still fighting something in the water. Maintain your shock level until you don't get an overnight drop, and then you should be ready to close the pool.

Thanks Aylad. That is very helpful. I cranked up the chlorine even higher last night. I had a small drop overnight from 36 to 35.5 this morning. CC is .5. Ph went up again, so your info is very helpful. Thanks.

Happy to help. If you're no longer losing more than 1 ppm of chlorine overnight, then you should be about ready to close :)

Update: After the algae was conquered, the pool took a long time to clear (even with vacuuming to waste). Putting some DE in the skimmer last weekend really helped (a tip I found on this site). I am happy to report that almost 2 months to the day after I bought the house and inherited this pool, I can finally see the drain. The pool store is closing my pool on Monday. I am looking forward to eventually doing that myself, along with doing the opening. But, I want to see it done first (I learn better that way). Thanks for your help.

Do yourself a favor and videotape (or at least audiotape and write down steps) the closing. It's amazing what details you can forget in a year's time, and forgetting steps can be disastrous :)