High Chlorine After Drain and Refill

[Jimbolo]

Good Morning Gang, Yesterday I drained about 3/4 of my pool and refilled it all last night and this morning. As of today I'm puck-free! Here were my numbers before the drain:

My test kit is a Taylor K-2005 (got it with the house, in good condition)
Free Chlorine - Too high to test. Water was dark pink, almost double the shade of the 5ppm comparator block.
CYA - Too high to test. Filling the small tube until the black dot was no longer visible left the water level about half way up to the 100ppm mark on the back of the tube.
Calcium Hardness - Too high to test. At adding R-0012 until the water turned blue, I stopped at 100 drops, which was about half my bottle.
TA - 120ppm
Ph - 7.6-7.8

After the drain and refill:

FC - about 7. A bit darker than the max level of 5 (at least I can measure it now).
TC - 5
CC - from -1 to -3
CYA - 70
Calcium Hardness - 320
Ph - 7.3
TA - 120

At least my numbers are in the ballpark now. But here's my question: Why is my FC still so high. My tap water is about 1-2. I shocked the pool on Thursday before the drain/refill, but since I couldn't measure FC I have no idea what level I shocked it to (put about a gallon of 10% chlorine in).

Is it possible there was some residual chlorine in the walls or filter that would cause my FC to still be high?

I should add that the change in Ph is due to the fact that during draining I used about a quart of muriatic acid to clean calcium off the border blocks.

Thanks for everything. Lifetime Supporter today!

Jim.

 

[JasonLion]

I don't see anything surprising here. Your FC level was extremely high before, and now it is lower. Your CYA level was extremely high before, and now it is lower. {EDIT}Ignore the rest of what I said.{/EDIT}

 

[Jimbolo]

Hi Jason, Thanks for the quick reply. I'm going to adjust my ph today. My CYA is 70. So you think my chlorine will drop of the next day or so to a reasonable level?

Thanks, Jim.

 

[duraleigh]

Hey, Jim,

I think Jasonlion misread your test results. A CYA of 70 is pretty high but manageable if you keep your FC high enough. In other words 7 FC with a CYA of 70 is not to high. In fact 6-9 would be the daily range where you need to keep the FC with that high CYA.

The rest of your numbers look pretty good except for that CC of 1-3ppm....You actually need to shock that out of your pool by bringing the FC up to about 20ppm and HOLDING IT AT 20PPM until the CC test result gets to be .5ppm or less.

If you would drain about 25% again of your pool, you will end up with a CYA around 50 and then find your FC much more manageable keeping it in the 3-5 range. Either way you still need to shock and get the remaining CC's out of your pool.

How does your water look?

 

[JasonLion]

I think Jasonlion misread your test results.

Indeed. I corrected my post.

 

[Jimbolo]

Thanks for all of the input. Actually my TC of 5, minus my FC (greater than 5, I think about 7) leaves me with a negative number for CC. Is this possible, and if it is, what should I do about it?

Thanks, Jim.

 

[JasonLion]

No, CC can not be lower than zero. When CC appears to be lower than zero it indicates a problem with your testing procedure.

 

[Jimbolo]

Hey Jason, So please help me solve this riddle then: When I fill the comparator with 9ml of pool water, then add 5 drops of 0001 then 5 of 0002, the color is a darker pink than 5. This number, whatever it is, would represent FC. Then I add 5 drops of 0003. That gives me TC. Adding 0003, for my pool water, ALWAYS lightens the shade of pink. This would indicate a lower number for TC than FC. So if CC = TC - FC, then I'm subtracting a higher number (FC) from a lower number (TC).

In my case I subtracted my darker pink FC (~7) from my lighter pink TC (~5), that gives me a number less than zero.

This has been the case even before my drain and refill. FC is higher than TC. The shade of pink gets lighter when I add R0003.

Any clues?

Thanks, Jim.

 

[JasonLion]

The test kit you are using is only valid for FC/TC levels up to 5. If the actual FC/TC level is above 5 the results are invalid.

This is the major quirk of the DPD chlorine test. It will show very high FC/TC levels as zero. If you were to slowly add chlorine to the sample, it would get darker and darker, and then it would get lighter and lighter again and eventually go clear when the FC level is high enough. That is why the test is only calibrated up to an FC level of 5.

 

[Jimbolo]

Now I'm really confused. I hate to be so dense about this. So if my FC being slightly darker than the 5 indicated makes the reading invalid, what do I do to get a valid test?

I have family in town this week so the answer as to whether I have a safe pool is rather important. The pool is crystal clear. I'll test FC again this evening when I get home. It will have been about 36 hours with no chlorine added at that point.

Thanks, Jim.

 

[JasonLion]

The best solution is to get a FAS-DPD chlorine test, which is good for FC levels up to at least 50. You can do the DPD test with dilution, but you lose a significant amount of precision. To test with dilution, mix equal amounts of pool water and chlorine free water (typically distilled water), do the test using that mixture, and then multiply the result by two.