I have the HC Phosphate Checker 713 that Ive had for 2.5 years. Today it read L.Lo when I put in my first vial after C1. After several attempts I change battery, cuvets, water sample, tried it with it open/closed, etc. Same results. Hanna says probably a bad light/sensor. and they have a one year warranty. Obviously not an option. Any one else have this problem and how did you solve? If nothing else i'll just have to purchase a new one. Thanks and reef on