Really strong bleach, or I did something horribly wrong

[Smykowski]

I've been on this forum constantly since last September, and I'm very comfortable with the basics practiced by everyone here (in theory, at least). Now, it's time for me to open my pool and get my hands dirty.

First test at 7:30 am:
FC 1.5
CC 0
pH 7.8
TA 180
CH 130
CYA 65

Added enough dry acid (using up the last of the pool store purchases) and MA to get the pH to 7.2, as part of my future plan to lower TA. Re-tested pH an hour later and it was right at 7.2. Water is hazy, but can see the bottom. Maybe a green tint, but only barely. I know I got junk in it last year while closing it, so I want to shock to start fresh. Based on a CYA of 65, shock level is 19. I decided to target 24 so that I would never go below 19 during the process. According to the pool calculator, I need to add 4.5 gal of 12.5% bleach to get to 24. Poured it in slowly, and started scrubbing/vacuuming.

2 hours later, tested to see where I was at...

9:45
FC 39!!!!
CC 1

What happened!?

I tested again at 11am FC 36.5 CC 0, and just now at 12:30pm FC 33 CC 0. Even though the numbers are high, they seems to be behaving correctly.

I re-measured my pool, and it might be 32' dia instead of 33', but that still can't account for that big of an error, can it? Along with the fact that a successful drain/refill for high CYA 2 weeks ago, and my pH test above indicates my size is correct.

This last time I did the test I went slowly and made sure the drop hung from the tip before falling. Can anyone think of anything I did wrong? Can the bleach be that "new"? Thanks.

 

[jblizzle]

Weird. I calculated 4.5 gallons as well to get to 24ppm ... so that seems right for a 25k gallon pool.

Seems doubtful that the chlorine was >20% to account for the discrepancy. I am puzzled as well.

 

[Smykowski]

Seems doubtful that the chlorine was >20% to account for the discrepancy. I am puzzled as well.

That's what I got too. Either that, I'm off on pool volume by about 8000 gallons (also unlikely), or my test accuracy at those high levels are a factor (although +- 10 drops is +- 5 ppm, and I'm still off by 10ppm from my target).

 

[steinholder]

were your jugs 182oz, instead of 128oz?

 

[JohnT]

You needed ~80 drops before the color disappeared?

 

[Smykowski]

I checked that too, it's the gallon bottles from Menards. I also made sure to look at the volume calculation, and not number of jugs output. (4.5 gal instead of 4.5 jugs).

Yep. 78 drops on the first go around. Am I forgetting something regarding special instructions with a high FC test or something?

 

[Smykowski]

Most recent test at ~2pm was FC 28 CC 1, so the pool is behaving as expected with regards to consumption/breakdown.

 

[Vinoveritas]

I had abnormally high FC readings for a bit, and then realized I used 25ml of pool water for the test instead of 10ml.

 

[Leebo]

Do the drops look the same size as they did at first?? Try to clean the tip with a damp rag before next test. There is a chance maybe there's a buildup on the tip causing the premeasured drops to be smaller, thus causing higher readings.

A long shot for sure....but a simple check that you should do every test anyways.

 

[Smykowski]

Used 10 ml every time.

As for drop size, I'm pretty sure they were all the same size, but I just did the test again, and wiped the tip to make sure.

Earlier this afternoon I got 28/1. We we going to be out all afternoon, so I put another 32oz of bleach in before I left the house, which should have brought it up to about 29.5 or 30ppm. I just tested again after I got home, and got 25/0. Again, very reasonable given the afternoon heat and sun, and the condition of my water.

I must have screwed something up this morning, but for the life of me I can't figure out what it is.

 

[Smykowski]

Update...

After three full days of shocking and never letting the FC get below 22, I'm convinced that it was the correct amount to put in. The pool behaved exactly as expected, including FC demand and results after dosing. I think I did the very first test WAY too slowly, and that's why it took so many drops to clear. I'm sure there were other small errors that were a factor (slightly more than a gallon in each jug, the fact that I'm testing for a level that's so high), but it was my first test - by trying to go slow and not screw it up, I screwed it up.

Good learning experience, though.

 

[linen]

From the extended test kit directions:

When measuring high FC levels, or measuring FC when the CC level is relatively high, it is important to move through the test quickly. Drops should be added about once per second, or slightly faster, swirling the entire time. You can slow down a little at the end of the test, to give you time to watch for the end point.

 

[Bama Rambler]

SpeedStir!

 

[Smykowski]

SpeedStir!

I've got the speedstir, that's not the issue. I was just so worried about drop size, I went waaaaaay too slow. I'm good now, though