unable to maintain chlorine levels

First, thanks for a great resource.

With only partial success, I followed the instructions given in a 2006 thread regarding repeated shocking and brushing until chlorine levels is stable for 24 hours. Achieved some positive effects in that my water is crystal clear and algae begins growing only after about 5 days. However, i never achieved a 24-hour stability. After 10 days (and 10 gallons of bleach) my generator was able to maintain chlorine levels for about 2 weeks. But, now the chlorine is once again disappearing as fast as the generator produces it.

Obviously i need to go back to shocking and brushing but I realize that I cannot trust the water tests from my local pool store. Different clerks give different readings every time. The thread mentioned you sell a complete water test kit, TF1100 (I believe), but i could not find where or how to order it. Please advise or send a link to do so. Until i have consistent readings i don't believe I'll ever fix this problem. Thanks much.

background:
20,000 gal in-ground, vinyl pool
Installed my 1st generator along with a new lining in February this year

Regards,

Coman

The TF100 is a modified K2006, modeled after the PS230 I used to sell. It's sold by another pool website. We recommend the straight Taylor kits. Link to the info page is in my blue signature block. It's very common for pool store test results to be all over the place.

Sounds like you've got a resurgent algae problem, and your SWCG can't keep up -- which is pretty typical.

+ Turn the SWCG off, and began dosing with 3 gallons of plain 8.25% bleach each evening. Brush after dosing, starting the 2nd evening.

+ Purchase a cheap OTO/phenol red kit, like these Walmart kits: #1 (preferred) #2

+ Test the pH and chlorine BEFORE adding the PM bleach dose. Skip if the chlorine level is DARK yellow to ORANGE. Double the dose if the chlorine level is very light yellow to clear.

+ Order the K2006 and report test levels when you have them.

thanks so much for the very quick reply.
Just to be clear: I'm to shock with 3 gals of bleach every day until the chlorine level stabilizes for 24 hours. AND, if there is a zero or very low chlorine level after 24 hours, then I shock with 6 gals of bleach. Do I have that correct?

should I be worried about the bleach raising the pH too high at this point?

I ordered the K2006 but deliver won't be until next week. I will report my readings to you then.

Again, thank you for your unbiased advice and knowledge.

It took a while but finally received my Taylor FAS-DPD kit. Here are my numbers as requested:

Free Chlorine (FC), ppm 3.0
Combined Chlorine, (CC), ppm 1.5
Protected Chlorine 48.0
PHMB
pH 7.6
Total Alkalinity, ppm 70
Calcium Hardness, ppm 70
Heavy Metals
Cyanuric Acid (CA, CYA, or Stabilizer), ppm 45
CYA Stabilization 55.15
Saturation index 0.55
Water Temperature 80

I’m still experiencing small algae recurrences.

Questions, if I may:
1. Which recommended guidelines is best to use, APSP or NSP, for my situation?
2. Which guideline should be use for total alkalinity, given a salt system… 80 to 100 or 100-120 ppm?
3. Please explain PHMB (listed on the guidelines) versus pH? The kit doesn’t test for PHMB. Should I bother with it?
4. How do I use the CYA Stabilization number? What is the min, ideal, max scale.
5. Ditto the Saturation Index?
6. My 80° water temp is unusually low now due to record low temps and rain this summer. Usually struggle to keep it below 90°. What is most important criteria to watch for when water temp is that high?
7. I’ve always been told Calcium should be zero or as low as possible in vinyl lined pools. True or not?

Again, thanks for sharing our considerable knowledge.

Regards,

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Originally Posted by Coman

Protected Chlorine 48.0
PHMB
Heavy Metals
CYA Stabilization 55.15
Saturation index 0.55

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Where in the world are these values coming from ??

calculated from formulas found in the test kit booklet.

What pages? I need to check it out.

took awhile to re-read the whole booklet, but...
Protected Chlorine: FC + Stabilizer -> Protected Chlorine, page 26
PHMB and Heavy Metals: in both tables, pages 43 & 44. No formulas/test procedures given.
CYA Stabilization: with Table K, page 63
Saturation index: see glossary and the instructions on the back of the Water Balance Calculator

Thanks for the page numbers -- I've printed that out, and will look at them.

. . . Now. Ignore all that stuff that I asked about; those are useless metrics.

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Originally Posted by Coman

I’m still experiencing small algae recurrences.

Questions, if I may:

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Quote:

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1. Which recommended guidelines is best to use, APSP or NSP, for my situation?

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Neither. Both include unnecessary calcium recommendations, and do not adjust chlorine levels for CYA level. (Do you mean NSPF?)

Quote:

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2. Which guideline should be use for total alkalinity, given a salt system… 80 to 100 or 100-120 ppm?

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Lower levels are less likely to scale.

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3. Please explain PHMB (listed on the guidelines) versus pH? The kit doesn’t test for PHMB. Should I bother with it?

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It's Baquacil. Ignore it. Had nothing to do with you.

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4. How do I use the CYA Stabilization number? What is the min, ideal, max scale.

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Ignore it. Read the Best Guess page, linked in my signature.

Quote:

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5. Ditto the Saturation Index?

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Ignore it.

Quote:

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6. My 80° water temp is unusually low now due to record low temps and rain this summer. Usually struggle to keep it below 90°. What is most important criteria to watch for when water temp is that high?

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Maintaining appropriate (Best Guess) chlorine levels.

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7. I’ve always been told Calcium should be zero or as low as possible in vinyl lined pools. True or not?

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Not true. On a vinyl pool you don't need to ADD calcium but you don't automatically have to lower it, either.

Quote:

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Originally Posted by Coman

Protected Chlorine: FC + Stabilizer -> Protected Chlorine, page 26

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Not an equation; it's a half-a'd way of expressing an idea.

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PHMB and Heavy Metals: in both tables, pages 43 & 44. No formulas/test procedures given.

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Not relevant to chlorine pools.

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CYA Stabilization: with Table K, page 63

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Ok. I'll have to explain. But the short version is, IGNORE IT!

LONG VERSION: With respect to pools, and most water treatment activities, alkalinity is the pH buffering over a specific range of pH values. (There are more technical definitions; you can Google if you want them.) Buffering is a measure of the resistance of a specific solution (YOUR pool water, in this case) to pH change over that range. In pool water, you have "TOTAL" and "CARBONATE" alkalinity. "Total" alkalinity looks at the absolute buffer status of your water; "carbonate" alkalinity looks at the proportion of the buffering caused by carbonates (HCO3, -HCO2, =CO2) in your water. Virtually all pool tests measure TOTAL alkalinity, not CARBONATE alkalinity.

Typically in pool water your TOTAL alkalinity is a combination of the buffering provided by borates (borax), cyanurates (stabilizer) and carbonates (pH UP, Alk UP, etc.). The index you are looking at attempts to estimate the cyanurate alkalinity, and then deduct it from the total alkalinity to approximate your carbonate alkalinity.

There's considerable debate whether this distinction is meaningful in concrete pools, or pools with gas heaters . . . but it is NOT significant in your pool.

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Saturation index: see glossary and the instructions on the back of the Water Balance Calculator

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SHORT VERSION: Doesn't really apply to you, but you might want to keep a negative-ish index, to avoid scale in your solar panels. PoolCalculator.com offers an easy way to do this -- but do NOT obsess over it!

LONG VERSION: The various saturation indices attempt to determine whether a given water solution is likely to deposit calcium scale, or to dissolve calcium products present (like water). This calcium index is, through a variety of arcane and doubtful deductions, then taken to offer some guidance about whether that same water is likely to dissolve iron (or perhaps, copper).

All of the indices (there are a bunch!), do some sort of mathematical jiggery pokery combining the water's temperature + pH + CARBONATE alkalinity + calcium hardness. There's been a bunch of discussion here (China Shop) and on TFP (The Deep End) about which index is 'best'.

Some of the college professors who were the original developers of these indicies, have cast doubt on their applicability to pool water . . . but that hasn't slowed pool chemical companies down. They *love* anything that gives
(a) a wizardly calculation that tells you to add more chemicals each time you visit, AND
(b) that can be performed auto-magically with a computer, calculator, or other electronic gizmo by pool store attendants who flunked junior high math,
(c) using dealer test results, whether they are accurate (titration) or mostly bogus (test strips).

A lot of people buy Taylor K2006, because of my Best Guess chart, my websites, and some 'me-too' sites. But, the K2006 is a small fraction of Taylor's pool business. They know who we are, and they know why we recommend what we do, but they also know that pool stores HATE what we do. And pool stores sell a LOT more of Taylor's overall product offerings, than all the BBB method websites out there.

So . . . Taylor stays on the NSPI / APSP / NSPF bandwagon because . . . they know which side their bread is buttered on!

Whew. Trying to wrap my head around a different chart.

So, if i read your chart correctly, for FC=3.0 and CYA=45, i should be OK. Right? Or, should i raise chlorine closer to 6 to suppress the algae growth?

How should I use your chart in conjunction with pH and TA measurements. if I understand you, those are the only 3 I need bother with. Correct?

BTW, thank you for taking the time to explain the long versions. I'm sure you've done it over and over. But it is very helpful. we budding backyard chemists appreciate it.

EDITED:

If you have algae, you should raise the chlorine levels to the algae level. Otherwise, it's not needed.

HOWEVER, losing chlorine suddenly tends to indicate beginning algae. I'd recommend going ABOVE the algae level for chlorine, then brushing the pool completely, and then holding at the algae level, until overnight chlorine loss is minimal.

With no stabilizer, pH levels have a big effect on the 'activity' of the chlorine present. After stabilizer, not so much. Alkalinity doesn't directly affect chlorine.

Regarding repetition: it takes a surprising number of repeated explanations to begin to optimize that explanation so that it usually communicates the key information effectively. But, this winter I am hoping to be able to 'migrate' a number of the oft-repeated (and now 'mature') explanations to static PoolSolutions pages, and just link them, from here.