Been reading here for a long time about deterioration of DPD powder. When it gets clumpy and dark gray or black, it's no good or maybe questionable. When in doubt, run an experiment. Taylor R-0870, same as in the PS-233 kit. Took a small amount from same batch and let it sit in a container, sometimes open, sometimes closed, in a high temperature and humidity environment (Northeast PA with no A/C) for probably 6 weeks. Looked awful. Did a 25 ml sample of water just now with good powder and yucky powder after declumping it. Both tests identical, 17 drops, 3.4 ppm. You can draw your own conclusion.
Al