Beginner's questions

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6amswimmer

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Feb 26, 2017
6
Pennsylvania
My TFT test kit arrived last week. I have scoured prior forums posts, but still have some questions.

1) I have a 2500 gallon indoor pool. I have added 20 ppm CYA. According to this website's chart, one should keep the free chlorine range form 3 to 5 ppm.
Can someone tell me what is the equivalence of free chlorine levels with 20 ppm of CYA versus free chlorine levels WITHOUT CYA? I have ultraviolet oxidation and the nature 2 filter ( I know the board doesn't like the copper component...) so I would like to keep a lower free chlorine level. The pool manufacture tells me I can keep a Free Chlorine of 1 ppm , but this is without CYA....I don't know how much FC I should maintain now that I have 20 ppm of CYA onboard?

2) What is the difference between muriatic acid and ph down? It seems most people here use muriatic acid. How come?

3) I have a combined chlorine level of 0.5. Does any action need to be taken?

Thanks,
George
 
Last edited by a moderator:
Welcome to TFP!

Please don't change the font colors, I can't see them on my device without highlighting them to change the background.

Without CYA the FC level is 1-3 ppm. But, the chlorine will be many times more harsh without CYA than with it. The CYA buffers the effects of chlorine significantly. I would use 30 ppm. There is no downside to CYA in your pool. I know it seems counter intuitive but FC at 1 ppm and CYA at 0 will be significantly more irritating to you than FC at 10 ppm and CYA at 30 ppm. And with CYA at 30 ppm you wouldn't be able to tell the difference between FC at 5ppm or FC at 10 ppm. What is irritating is the CC. Any CC above 0 can bother people with the "chlorine smell".

In a spa/hot tub type environment, which yours basically is, the key to effective chlorination is to add enough chlorine so that the next time you add chlorine there is still chlorine in the water. You never want FC to drop to zero because bacterial colonies can double every hour or so in low chlorine conditions and the water will quickly start to cloud up with bacterial colonies. Keeping some notes of before and after testing of FC will help to see the pattern. After swimming add FC, test a couple hours later to make sure it didn't all get used up. Add more if needed. Then test a few hours later and again the next day. Depending on the usage pattern.

Dry acid is sodium bisulfate, it adds sulfate to the water which can accumulate and shorten the life of heaters and SWG cells. It also costs quite a bit more.

Usually the solution to CC in the water is a little bit more chlorine. CC builds up due to insufficient chlorine. Free Chlorine burns of CC. Leaving it uncovered for a while will also help.

Copper in the pool will build up and eventually stain surfaces in the pool and tint light hair, fingernails, towels, dogs, etc green. The copper does not allow lower FC levels because copper doesn't sanitize the water or kill bacteria. Copper does have some ability to inhibit algae growth but in a tub that is covered most of the time that isn't much of a risk. And the chlorine will kill algae more effectively than copper will slow it.

UV does sanitize some of the water as it moves through the UV light but there is no residual sanitizer effects in the rest of the water so chlorine is still required at pretty much the same level.
 
Oops thanks for the feedback about font color !

You mention that for a spa/hot tub environment that the key to effective chlorination is to add enough chlorine so that FC never drops to zero. The CYA/Chlorine chart says that at 30 ppm CYA, one needs a minimum of FC of 2. So for a hot tub/spa, is our lowest number for FC 2 or can I try to shoot for a target of say 1 ppm for FC? I know I'm paranoid, but I worry about the health effects of chlorine, whether combined or free -- I would like to keep free chlorine as low as possible. I guess I'm trying to understand the rationale for how the number of 2 ppm for minimum free chlorine was derived.

Thank you for your other explanations, especially in regards to the deleterious effect of sulfate from pH down.

Thanks,
George
 
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