How long should bleach shock last?

[timmy2]

First, greetings to this group. I'm thrilled to find a forum for DIY pool owners and will try to contribute when I have something substantive to add.

But at the moment I have a question and hope someone will respond.

Green pool. 26K gallons. In-ground, fiberglass coated.

Yesterday's measurement said:

FC 1
TC 3
PH 8+
ALK 120
CYA 0

I own and have successfully used PoolProfessor Software for a couple of years. It said I needed to add 2.5Gallons of Sodium Chlorite first, whereas normally I use Home Depot Cal Hypo. In my search to find out what Sodium Chlorite is and how to buy it cheaply Google revealed your site to me. I read for a while and then bought 3G of Chlorox "Standard, Original" bleach (6%) at Sam's Club. I dosed the pool last night.

This morning it still measures the same. Where did I go wrong?

Secondly, I have had a dark blue porous cover over the pool all winter. My uninformed conclusion was to leave the cover on until I get the water in better shape, because I figure CL won't burn off as fast when it's covered. Is this stupid and should I remove the cover for the battle ahead?

[duraleigh]

Hi, Tim,

Can you test for Calcium Hardness? If so, post that result right back.

Your first priority should be to get your pH down into a 7.2 - 7.6 range. Put that in front of any other thing you do to the pool and do it reasonably quickly. This evening would be ideal.

Secondly, you did nothing wrong with the Cl. The vast majority of it was gobbled up by your green (algae) water and, if there was a trace left at sunrise, the Sun quickly consumed the rest because there is no CYA in the pool to protect it.

After you get your pH corrected, I would put 6 gallons of 6% Clorox in the skimmer at dusk and run the pump 24/7 from that point. Your Cl will probably be zero or close to it the next AM. The next evening, retest for pH and Cl and add enough Clorox to get up to about 12-14ppm. It'll probably be gone by at least midmorning. Repeat this process 'til your pool clears, backwashing when necessary, Tim, the only way this works without taking more than a week is if you keep the Cl up in that high range at least every evening. You can bring it up to that level as many times as you like during the day but the Sun depletes it rapidly.

As soon as your pool holds a decent Cl level overnight, you'll probably want to backwash once more and then add your CYA...6lbs should get you around 30ppm. You may want to add some more but not for a week or so.

Oh, yeah. Take the cover off...everything will get better.

[timmy2]

Thank you for replying! Very kind of you.

After posting my question I kept reading posts in this forum and found a thread where the advice was to add CYA before continuing to add bleach. But your advice entails adding the CYA at the end. Interesting.

While picking some CYA up at Home Depot tonight, a guy who said he works on pools, stopped and cautioned me that I really should think twice about adding any. Something about it being outlawed as carcinogenic in some states and generally that it's rarely needed. I'll have my water checked at the pool store tomorrow just to verify my own tests. The two tests I've done indicate it's very low.

I really do appreciate your thorough explanation. Sam's Club's Clorox is relatively cheap so I'll try your approach for a few days. I'm curious about what will change to enable the Cl to remain up if I don't add CYA.

[Maxout]

Your "guy that that works on pools" is just spreading old and bad info that is kept alive by the purveyors of "super non-chemical" (subtitute miracle) water sanitation systems, most of which are dubious at best. It's always "I heard that" or "in another state/country", "the government is about to" etc.

http://www.intox.org/databank/documents/chemical/cyanacd/cie286.htm

[duraleigh]

Hi, Tim,

Please disregard the advice you received from the bystander. He is wrong.



Sam's Club's Clorox is relatively cheap so I'll try your approach for a few days. I'm curious about what will change to enable the Cl to remain up if I don't add CYA.
Nothing. Your Cl that you add at dusk will work on the organics at night and be killed off completely by the Sun the next AM. The CYA protects the Cl from the Sun to an extent.

The issue is that if you put in CYA now, it sits in your filter and dissolves over several days.....you should be backwashing during those several days so you will simply backwash your undissolved CYA out of the pool.

Reread the method. Cl at night to protect it from the Sun, then CYA when your pool is clear and you've finished the frequent backwashing.

Many, many, many folks, "try" this method for a few days and fail. They simply underestimate the amount of Cl needed to sanitize the pool. They "tiptoe" up on the problem rather than hitting it with a baseball bat.

Test and add Cl...Test and add Cl....Test and add Cl. :) :)

[waterbear]

It is true that some localities have outlawed CYA in commercial pools but these pools usually have chlorine feeders and ORP controllers to manage chlorine levels. CYA DOES mess up ORP readings but since you are not using one it becomes a moot point. As far as the dangers of CYA vs. the benefits....The dangers of swimming in a underchlorinated pool are very real and have been well doucmented. The 'dangers' of using CYA are not. To my knowledge there have been no human stuides on the carcinogenic properties of CYA and animal studies have been inconclusive. If I am wrong someone please correct me!