22 gallons of bleach and I can't get my chlorine above 5

[cscannon]

So I read about using bleach to shock. My CYA is 20 so according to the table, I can shock with a FC of 12.

Over the last three days and multiple trips to the grocery store, I have added 22 gal of bleach to my 30,000 gal pool. Yet my chlorine is barely 5!.

I am using sodium hypochorite bleach and the bottle doesn't give a concentration but if it was 6% shouldn't I have a chlorine level of like 40?

My pool is uncovered and I recognize the the UV is degrading my chlorine with such a low CYA (I was going to add the CYA after the shock) but surely it doesn't disappear that fast?

Any thoughts? With the $ I've spent on bleach so far, I could have bought shock from the pool store which I'd sworn I'd never visit again.

Thanks,

Steve

[chem geek]

You can always measure your overnight chlorine loss to see if the loss is only due to sunlight. With only 20 ppm CYA, you could be seeing losses of 60-70% of the FC in a day, but the CYA test could be off a bit so losses could be even greater (if there were no CYA in the water, then half of the FC gets broken down every hour in direct noontime sun in a pool with typical depth -- in very shallow water, half gets broken down every 35 minutes). Even so, I suspect there are other issues here. You could add the chlorine at night, have the pump circulate for an hour, test the FC. If it's not what you expect, then the chlorine isn't as strong as you think or there is something in your pool consuming chlorine quickly. The overnight drop will tell you if there is something in your pool using up the chlorine other than sunlight.

You can also test your chlorine's strength by knowing that 1/4 teaspoon of 6% bleach in 2 gallons of water is 10 ppm FC. Use distilled or filtered water if you have it -- if you use tap water, then account for the initial FC or CC.

[CarlD]

How are you testing your water and how often?

Are you using strips?
If so, you may have bleached them out!

Are you using DPD? If so, very high FC levels bleach out that test as well! Plus you should be testing your TC levels as well (Total Chlorine).

If you are using FAS-DPD to test your chlorine, you should be testing your CC levels as well (Combined Chloramines).

Since TC = FC + CC, in both cases you should see if you have a measurable CC level.

What is your pH level? That, too affects chlorine.

[cscannon]

Thanks for your help. I had absolutely NO idea that chlorine would disappear so quickly without CYA. Prior to this year, we've always had a cover so I've never had this problem. This year we replaced it and after they took our old one off, they found that the new one wasn't the right size. So now we have nothing.

I am using a Taylor DPD test kit. When I first opened my pool a week ago my pH was 8.0. (I wasn't very faithful about testing it during the winter.) I added enough muriatic acid to bring the pH down to 7.3. A couple of days later I started adding the chlorine. As I did so the pH was going back up and is currently at 7.8. I ignored the high pH thinking that as soon as I was done with the shock I'd be adding CYA which I figured would be lowering the pH. Then I could add whatever muriatic acid was needed after that. TC doesn't seem to be any higher than FC.


Thanks,

Steve

[Watermom]

If your TC is equal to your FC that is what you want because it means that your CC is zero, which is the goal. Until you have an adequate amount of cya in there, it is usually necessary to add bleach morning and evening. (and in some cases, even in the afternoon.)

[cscannon]

What is the relationship between pH and chlorine?

Steve

[chem geek]

What is the relationship between pH and chlorine?
Steve, I don't understand the question. Do you mean if there is a change in chlorine effectiveness with pH? There is, but not as much as those in the industry claim because CYA in the water minimizes this effect so I wouldn't worry much about that.

Do you mean will pH affect the rate of chlorine loss? The answer is yes, to some extent, because higher pH means more of the form of chlorine that breaks down faster in sunlight compared to the form that dominates at lower pH. However, with a lot of CYA in the water, this effect is secondary -- it's mostly seen when there is little CYA in the water such that a combination of no CYA and high pH results in quite rapid loss of chlorine in sunlight.

[cscannon]

My question was in response to CarlD who commented, "What is your pH level? That, too affects chlorine." You've answered that question, thanks.

[CarlD]

That's the other side of the coin. Chem_Geek is explaining how too high pH can reduce chlorine's effectiveness.

However, what I was referring to is that when chlorine levels are very high, pH can appear higher than it really is. Chem_Geek's gone into a thorough explanation of this in other threads. That's why chlorine neutralizer is needed then prior to the pH test.

[cscannon]

Got it thanks!