Shock question

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TomAtlanta

Well-known member
Sep 10, 2011
392
Atlanta Ga
In pool school shock instructions it says:

Repeat steps 1 and 2 as frequently as practical, but not more than once per hour, and not less than twice a day, until:

CC is 0.5 or lower;
An overnight FC loss test shows a loss of 1.0 ppm or less;
And the water is clear.
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The water is clear of algea but it is still a little cloudy. I assume that cloudyness is dead algea. Last time my pool guy shocked it, he just did the shock once and told me to run the filter for a few days until it cleared up. I did that and it worked fine.

Are you saying that it is better to keep adding chlorine every day until the filter clears the water?
 
Keep adding chlorine until the algae looks dead, as yours does, then perform an OCLT to verify you are done. I wouldn't continue with the shocking because of a little cloudiness after an algae fight if you are certain it is dead. Keep filtering 24/7 and brushing to clear the water though.
 
Assuming you maintain good chemistry and your algae is really gone, it's just a matter of removing the dead algae. If there is a significant amount on the bottom, vacuuming should help. If there is just a little, stirring it to help the filter pick it up will help. Whatever it takes to get the dirt to go through the filter.
 
TomAtlanta said:
So just brushing and filtering should clear the water, right? Last time it got clear even without the brushing but brushing couldn't hurt. A friend told me I should also vacuum, but is that really necessary?
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You need to pass the Overnight Chlorine Loss Test. That tells you if there is anything consuming the chlorine in the dark, so you know that means organics (algae, typically) in the pool. Instructions in Pool School, and elsewhere in the forum.

You brush because algae can regrow under the cover of the dead algae where the chlorine cannot get to it.

Filtering clears the water of dead algae.
 
The procedure we suggest for shocking is to raise your free chlorine up to shock level (level will depend on how much CYA you have in your water) and hold it there or slightly higher until the algae is dead. You can tell this with an OCLT (overnight chlorine loss test) to see if you loose less then .5 FC overnight (dark to pre-dawn). The typical pool service approach is to boost your chlorine level WAY above shock level so that it hopefully does not drop below shock level until all the algae is gone, there are a couple of big down sides to this method, one there is that guess about how much chlorine will be needed to do this, guess too low and your back where you started in a week, then their is the bigger issue, that super high chlorine level shortens the life of your pool equipment (harm seals on pumps, bleaches out vinyl liners, etc.) It is also wasteful on chemicals, but that is not a big concern if your in the pool service business.

The thing to remeber as a pool owner your concerns are most likely what is the best for the pool, and what makes the water healthiest for your family, pool service companies want what is easiest on them, perfect water quality, and long term damage damage to the pool are not anywhere near the top of their list, and pool stores want to sell as many chemicals as possibile, any claim to the best water conditions are just there by chance as they want a happy customer (a happy customer is often uninformed customer).
 
Thanks for the info.

You say that super high shock chlorine levels wear out the pool faster. How about slightly high every day chlorine levels? I realize that none of these chemistry tests are very precise, espicially the daily chlorine level based on shade of yellow, and the CYA test. My CYA is somewhere between 40-50, I think, but I get different results on different days, maybe based on the quality of my vision and judgement on different days. The lady at the pool store has also given me different levels on different days. I also know the chlorine test based on color is not accurate, and I don't want to do a drop test every day. I got a bad algea overgrowth because I thought my chlore was at 5 based on the daily test, but then did a drop test and it said chlorine was only 2. Is there any reason not to keep my daily chlorine up around 8-10 just to make sure?

Second question. Where do I get a quick chlorine test kit based on shade of yellow that goes higher than 5?
 
TomAtlanta said:
You say that super high shock chlorine levels wear out the pool faster. How about slightly high every day chlorine levels? I realize that none of these chemistry tests are very precise, espicially the daily chlorine level based on shade of yellow, and the CYA test.
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That test is designed to primarily check the presence of FC. Like you said, it will not be terribly accurate.

TomAtlanta said:
My CYA is somewhere between 40-50, I think, but I get different results on different days, maybe based on the quality of my vision and judgement on different days. The lady at the pool store has also given me different levels on different days.
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Pool stores OFTEN have inaccurate results...especially for CYA. I would rely on drop testing myself for the CYA readings.

TomAtlanta said:
Where do I get a chlorine test based on shade of yellow that goes higher than 5?
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A FC test that will accurately measure above 5ppm will be a FAS-DPD test (not the OTO yellow-matching test). The TFTestkits TF-100 and the Taylor K-2006 come highly recommended here.
 
I have the TF-100 and do the FAS-DPD test. I just wondered if there was a way to avoid doing it every day with a quicker simpler test, but I guess there is not.

One unanswered question - Is there any reason not to keep my daily chlorine up around 8-10 just to be safe? I know this is high for my CYA, but other than a little extra expense for chlorine, is there any reason not to keep your daily chlorine high?
 

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TomAtlanta said:
I have the TF-100 and do the FAS-DPD test. I just wondered if there was a way to avoid doing it every day with a quicker simpler test, but I guess there is not.
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Great test kit! Normally, you will only need to do the FAS-DPD test when you are shocking.

TomAtlanta said:
One unanswered question - Is there any reason not to keep my daily chlorine up around 8-10 just to be safe? I know this is high for my CYA, but other than a little extra expense for chlorine, is there any reason not to keep your daily chlorine high?
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Technically you could swim at shock levels, so I don't think this would cause problems...except to keep it that high, you would constantly be using you FAS-DPD test and will run out of reagents faster. Also, seeing that the recommended levels (pool-school/chlorine_cya_chart_shock) put you in the 2-4 range, having FC of 8-10 would be overkill. If you keep it at 4 (or even 6 if you want to be extra safe), you should not get any algae blooms.
 
Also, seeing that the recommended levels (pool-school/chlorine_cya_chart_shock) put you in the 2-4 range, having FC of 8-10 would be overkill. If you keep it at 4 (or even 6 if you want to be extra safe), you should not get any algae blooms.
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I said that my my CYA is somewhere between 40-50. That puts me in the 3-6 range doesn't it? 3 is the minimum for CYA 40, and 6 is recommended for CYA 50. Did I miss something?
 
I did the shock and passed the OCLT.
That was only 8 days ago, and algea is growing again.
The only thing I might have done wrong is that I did the OCLT after the shock was over. FC was up to 20 at one time, CC was 0.5 and water was clear , but when I did the OCLT it was 2 days later and FC had already gone down to 16.5. The next morning it was 15.5.
I am shocking again.

FC 6.5
CYA 40-45
TA 60
Calcium 280
 
Have you positively kept your FC at or above the minimum recommended for your CYA?
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Yes I have. 6.5 is as low as it has gotten and CYA is under 50 for sure.
The only thing I can think is maybe I am doing some test wrong. The FC test says to use a heaping scoop of R-870. What exactly a heaping scoop is could vary. The CYA test is confusing to me, but I know for sure that I can still easily see the dot at the bottom at 50.
 
Circulation problem could be it.
I notice the algea is forming on one side of the steps but not the other side.

The skimmer is the only thing sucking water from the pool. The sucker at the bottom was sealed up because of a leak. (Is sucker the right term?)

I have not been brushing it regularly. I wonder if brushing it more would do any good.
 
This page http://www.taylortechnologies.com/Chemi ... ntentID=44 has photographs which show what the view tube looks like when the test is complete.

You may want to remove or access anything that has water behind it, (like a light) and clean. I had a similar experience to yours last year, which ended when I removed my light, cleaned the niche and left it all exposed during the superchlorination process.

So far as brushing, I have been told nobody brushes enough. I don't know if it is true, but it does stir things up and seems to help in my pool.
 

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