Testing Problem?

[wrems]

I tested my pool this morning before cleaning it or removing the solar cover. The pump had been running about an hour:

FC 3
CC 1
PH 7.6
TA 80

So I added 25 oz bleach according to pool math (8.25% just to bump 1ppm). I also added half of the borax to bump my pH to 7.7. That was about 14 oz by weight. Just trying to nudge it. This is based on 17k gallons not 19 like in my signature. I also threw a sock of CYA in the skimmer as I’m in the low 40’s and trying to creep up on 50.

I proceeded to clean and vacuum after adding my chemicals and cover was removed. Then I left the pump running and the cover off while I ran some errands. I came back and tested again to see if my pH and FC were at my expected values of 7.7 and 4.

My 2:30 readings:

FC 5.5
CC .5
PH 7.6
TA 80

My FC increased by 2.5? That doesn’t make sense to me… I was at 3 added a measly 25 oz and went up 2.5ppm? I’m not at all surprised my pH held. I pretty much expected that to still be 7.6.

How can my 2.5ppm uptick be explained? I’m using k-2006, speedstir and sample sizer.

 

[jblizzle]

There is no reason to try to keep tweaking the numbers like raising the pH from 7.6 to 7.7. Odds are the pH will rise on its own.

As far as the FC:
1. Strong bleach?
2. Smaller pool?
3. Testing error?
4. Combination of the above.

 

[wrems]

Actually, just checked the bleach. It's labeled as 6%! From Walmart, I thought I had grabbed 8.25%. I need to pay closer attention. I thought that about the size that's why I changed my calculations to 17k instead of 19k. I guess I better go measure instead of listening to the pool store on size...

 

[wrems]

Poolmath has my pool about 18k gallons. It's a 16' x 34' oval with deep sculpted side walls on deep end. It's about 8' there and 3' on the shallow end. The shallow end has pretty straight walls. The deep end the walls really cut into the bottom of the pool. So my 17k guesstimate is probably pretty close... I still can't figure out how my 25 oz 6% bleach moved my FC by 2.5 ppm. Unless, I totally screwed up my reading this morning.

 

[jblizzle]

Does not really matter what happened in the past ... just keep moving forward.

 

[duraleigh]

You must make sure you reach the endpoint of the test each time. You continue to add drops until the last drop you add makes NO FURTHER color change whatsoever. Then you subtract that last drop from the total and the result is your FC. All color change tests in the TF-100 must be done the same way.