YSI pHotoFlex pH [251100Y] LED Handheld Colorimeter. The pHotoFlex line of colorimeters is the newest addition to YSI's full range of colorimeters. These rugged, waterproof, multiparameter colorimeters are ideal for laboratory and field testing. Receive 20 free packets of DPD Free Chlorine or DPD Total Chlorine! Get your free samples. Interested in a pHotoFlex colorimeter? Learn about the trade in program currently going on (U.S. only). Or, if you prefer to buy from one of our dealers, take advantage of our rebate program!.  The instruments feature a large, backlit display, waterproof rating, data logging with the ability to export data to a computer using LSdata software, user-defined programs and a 2-year warranty.