unable to maintain chlorine levels

[Coman]

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

[PoolDoc]

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.

[Coman]

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.

[Coman]

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,

[PoolDoc]

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

Where in the world are these values coming from ??

[Coman]

calculated from formulas found in the test kit booklet.

[PoolDoc]

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.

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?

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

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

Lower levels are less likely to scale.

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

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

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

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

5. Ditto the Saturation Index?

Ignore it.

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?

Maintaining appropriate (Best Guess) chlorine levels.

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

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

[Coman]

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.