I don't fully understand the explanation for myth #11 from this article: http://ppoa.org/?page_id=418
11. When a DPD chlorine test flashes a little pink then turns crystal clear, your water has almost no chlorine in it.
The opposite is true! More spas are fried and bathing suits bleached because of this error than just about any other. As you know, the universally accepted DPD test for chlorine turns progressively more pink as higher residuals are encountered in the sample… that is until the indicator is itself reverts to a clear resultant. This phenomenon occurs somewhere near 20 ppm chlorine, the actual value varying with different pH or total alkalinity conditions. Many, many untrained operators or “helpers” have dumped excessive amounts of chlorine in their water (most often in hot whirlpools or spas), thinking all along that for some crazy reason they just hadn’t yet put enough in to get a reading! In a small body of water this testing error has resulted in a few hundred parts per million chlorine residual, creating some very unsafe, damaging or at least unpleasant conditions.
While my pool is stable, now, as I set up my pool 2 weeks ago I had to add excessive amounts of chlorine to keep my pool at the proper levels. At first, I attributed the disappearing chlorine to the really hot days without a pool cover and not enough cya and then thought maybe I had an algae issue that was lurking in the pump/equipment. Since the pool was taken out of storage and reset up with fresh water I don't even know if that is possible. I added chemicals approx. 4 or 5 hours after the pool finished filling. Now after reading the above information which I don't quite understand, I wonder, if somehow, I had high levels of chlorine even though the pool water in the vial would stay clear after I added the dpd testing powder. (I should mention that the oto test was also showing clear!) I, also, noticed a pair of shorts I swam in that were black faded to grey really fast. ( Although these are not meant for swimming and might not be very colorfast.) Is the article referring to the same test using the dpd testing powder? I use the Taylor R-0870 powder, then if it turns pink I use the R-0871 FAS-DPD titrating reagent and then I use the R-0003 DPD reagent and if it turns pink then I use the R-0871 FAS-DPD titrating reagent once more.
What do you more knowledgeable fellow pool lovers think?