FAS-DPD and Speedstir -- strange results

[PoolDoc]

Hm-mh.

My own, very informal testing, has never shown much of a difference between surface and 6""+ down. But, if the surface is covered in goop, including suntan lotion slime, I always go deeper. If you want to go a step further, it would be interesting to know if there actually is a detectable difference between surface and immediate sub-surface.

One other note: on pools under full sun you would expect to see a difference in chlorine levels between the surface and 12" down, if the CYA level is zero. Half-life at the surface can be as little as 15 minutes.

[tpspeier]

Our pool is in full sun, but the CYA level is around 110-120 (I used the distilled water trick mentioned in a thread on this forum to measure since it was above 100) so I would suspect little difference in chlorine levels between the surface and below the surface. I may try the depth experiment once I resolve the Speedstir vs. manual-swirl variation.

[tpspeier]

I finally did through step #5. The results were about the same: 24 drops for the manual swirl and 18 drops for the Speedstir. I now have the gallon of pool water covered to test tomorrow.

[PoolDoc]

Thanks.

You're going about it carefully enough, so that no matter what result you get, it will be helpful info for many.

[tpspeier]

Results of step #7 are about the same: 24 drops for manual swirl and 17 for the Speedstir.

For steps #10 and #12, does it matter if I use yesterday's pool water from the gallon jug or if I take a fresh sample?

[tpspeier]

I tried the first step #10 from Ben's list with the same results. I tried several other experiments involving varying the drop rate on the two samples, but all of those showed the same results too. I forgot to try the second step #10.

On the bright side, the pool is crystal clear and we've really been enjoying it.

[chem geek]

Have you tried slowing down adding the drops to the SpeedStir so that you take as long for the two tests? Also, if you let the SpeedStir water set still after the test, does it turn pink again after a minute or so? I'm just stumped.