Using Bleach in the Pool

[Schooled by 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?

[aylad]

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!

[CarlD]

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.

[aylad]

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

[Schooled by Pool]

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.

[aylad]

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.

[Schooled by Pool]

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.

[Schooled by Pool]

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

[aylad]

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.

[Schooled by Pool]

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?