Funny story

[MITBeta]

Yesterday afternoon I found a length of 1/2" PVC in the garage, cleaned it, and marked it at 24" from the bottom to use as a dip tube for water sampling.

I used it to fill my sample bottle and then started in on my weekly, full set of tests.

First test: FC 13. That's odd, I thought. It should be between 6-8 since it was 6 at 10:30pm the night before and I added 800ml of 12.5% bleach to raise it 2ppm.

So I dump the sample out and re-test. 13 again.

I ask my wife: You didn't add any chemicals to the pool, right? She looks at me like I have 6 heads. That means "no".

So I dump my sample in another container and go take a sample the normal way: upside down container, elbow deep. FC 7.

Hmm.

Thoughts that went through my head: Is my pool mixed so poorly that the difference between elbow height and 24" could be 6ppm? Did I add 4 times more bleach than I thought? Is the bleach stronger than on the label? What gives?

Then it came to me. The answer is in the first line of this post: I cleaned the PVC. What with?

Bleach.

The residual bleach, despite spraying the inside out with the hose, was enough to affect the same.

We had a good chuckle about it. I hope you do, too.

 

[mguzzy]

Welcome to sample techniques 101! When I was in Grad school for Marine Science there was a story the profs always told about sampling from the side of the boat.. On one particular research project, the first water sample on the line of samplers always came back with higher iron.. it didn't fit the depth profile of the other samples.. Turns out the first sample bottle was taking water too close to the hull of the boat.. who-da figured.

nice job of deduction!