Bad dpd powder??

tadcpht

Well-known member
Jul 17, 2012
95
Forest, VA
My pool has been burning through some chlorine the last two days and the deep end was a touch cloudy, so I did the OCLT test last night and lost 1-1.5 FC. So I figured I should start a SLAM. I tested this afternoon
FC 3.5
CC 0.5
Cya 50
Alk 110
pH 7.5
According to cya I needed to bring up to 20. So I added 2 jugs of 8.25% bleach. Waited 45 mins and retested. Halfway through the test (20 drops) the sample turned dark grey or black. I kept adding drops up to 40 and no change in color. It was bright magenta to start. Dpd powder is a few years old. Is my powder bad? Also tested cya after bleach and it said 40. Does the bleach affect the cya test? If not what can account for this? I need a solid cya number so I know what bleach to add. Please help and thanks for any replies.
 

BoDarville

TFP Expert
LifeTime Supporter
Jun 5, 2012
3,844
DFW, Texas
Bleach will not affect the CYA test. The CYA test is one of the more subjective tests. Proper lighting is crucial when performing this test. Suggest referring to the Extended Test Kit Directions - see post # 8.

If your DPD powder is a few years old, I would suggest replacing it with a fresh batch. In all the years I have performed this test, I have never had the sample turn grey / black.