Why would one need to perform an OCLT if they have a CC test?

DaciaT

Member
Jun 17, 2019
14
Breaux Bridge, LA
Please explain why one would need to perform an overnight chlorine loss test to determine if there is a potential problem in their pool such as algae. If the CC test is below 0.5, is that not a solid indicator that there isn't a problem? Could one have consistent CC readings of zero, yet have an underlying problem that an OCLT would reveal?
 

ping

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Jun 24, 2011
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Long Beach, CA
No, I've had to SLAM even though my pool showed 0 to .5 CC's even though the pool was full of algae. CC's don't always show up if you are battling algae.
 
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JoyfulNoise

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May 23, 2015
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Tucson, AZ
CCs are not necessarily elevated when algae is present. CCs form from the reaction of ammonia and organic amines with chlorine. The sanitizing reactions that kill algae may or may not produce much CCs at all. Chlorine loss in the absence of sunlight is the best indicator of algae.
 

zea3

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Jul 10, 2009
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Houston, Texas
Also CCs are constantly being created and broken down as part of the oxidation process. Just as 0 CCs don't necessarily indicate 0 algae, a CC of .5 doesn't necessarily indicate the presence of algae.
CC formation is part of the oxidation process, but you could be oxidizing swimmer waste, sunscreen, leaves, or the latest pool store magic potion. The OCLT is the best indicator of a nascent algae bloom.
 
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Donldson

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Jun 12, 2009
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NW Ohio
I am really at a loss as to where this whole "No CC = No Problem" idea comes from, but it seems to be a pretty common misconception unfortunately. It's like a fever: if you have one then you are probably sick but if you are hacking up phlegm and have a sore throat then the lack of fever doesn't mean you aren't sick. CC is just one parameter in diagnosing a very specific pool problem and the lack of which rules only those very specific problems out. A lack of CC never rules out algae, nor does the presence of CC indicate algae.

As I posted recently, credit to JamesW:

Many people doing a SLAM for algae expect to see CC as part of the process.

However, algae should not react with chlorine in a way that creates CC.

CC is a result of chlorine combining with something like ammonia where the chlorine is still in the active +1 state.

For the most part, the reaction of chlorine and algae is an oxidation reaction with the chlorine being reduced to inactive chloride in a -1 state.

If CC is present, that usually points to some contaminants in the water.
 
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DaciaT

Member
Jun 17, 2019
14
Breaux Bridge, LA
I guess we all are lumping algae together with "contaminants". But yes, I was DEFINITELY in the camp of "No CC = No Problem", even after spending hours and days poring over this website, studying and reading and embracing and firing my pool store. My pool has looked "suspicious" (cloudy...but colorless) for several days, I was suspecting an issue with my filter because my CC was zero. I let the FC drop too low on 2-3 separate days over the past 10 days. Now I have slimy walls. Crud.
 

DaciaT

Member
Jun 17, 2019
14
Breaux Bridge, LA
Listen I don't have a firm CYA reading anymore because I'm out of test kits for CYA. I was maintaining it at 40 before losing about 6" of water early July. Since then I've guessed based on daily chlorine loss, and subsequently added stabilizer to bring it up by 20. For a SLAM, would it be a good workaround to over-shoot the CYA level and over-chlorinate if you're not sure, as opposed to under-guessing the CYA and under-chlorinating? (The answer seems obvious...but is there a disadvantage to over-chlorinating that I should be aware of?)
 

duraleigh

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I am really at a loss as to where this whole "No CC = No Problem" idea comes from, but it seems to be a pretty common misconception unfortunately.
I think it comes from a test result of 1 CC or greater indicates a problem so (it would be easy to assume) a cc test of ZERO would indicate there is no problem.......almost logical but very incorrect.
 
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zea3

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Houston, Texas
Listen I don't have a firm CYA reading anymore because I'm out of test kits for CYA. I was maintaining it at 40 before losing about 6" of water early July. Since then I've guessed based on daily chlorine loss, and subsequently added stabilizer to bring it up by 20. For a SLAM, would it be a good workaround to over-shoot the CYA level and over-chlorinate if you're not sure, as opposed to under-guessing the CYA and under-chlorinating? (The answer seems obvious...but is there a disadvantage to over-chlorinating that I should be aware of?)
In order to have dropped your CYA by 20ppm when you lost that 6 inches you would have had to have lost 1/2 the volume of your pool. I suspect the amount of CYA you lost was negligable, and by raising it by 20ppm you are now in the 50-60ppm zone. If my suspicions are true you have been under chlorinating your pool, which is why it became cloudy. Cloudy water is a sign of a nascent algae bloom. The soft sided pools like you have don't have the traditional vinyl liner. Soft sided pools are made of a tougher material, however they will fade with if the chlorine levels are too high for too long. In order to successfully slam your pool you will need to be able to measure your CYA to get a starting slam level, and you may need some refills of your FAS/DPD kit. You could get another HtH 6 way kit, or you could order the CYA test from TF testkits.net CYA (Cyanuric Acid) Test It should have enough tests to last you the next 2 seasons.
 
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