The specific storage conditions greatly influence the lifetime of some of the reagents. If stored properly everything can last two or three years. However, some reagents can go bad much more quickly if they are subject to prolonged high temperatures, freezing, direct sunlight, or frequent wide temperature swings. In the test kits we recommend, the FAS/DPD titrant (R-0871) is the most sensitive to aging. It should be a colorless liquid, but will turn dark yellow when it goes bad. The PH, TA, and CH indicators (R-0004, R-0014, R-0008, and R-0011L) are the next most sensitive. All of them will stain their plastic bottles when they start to go bad. The FAS-DPD powder (R-0870) will get darker and start to clump up when exposed to moisture, but is usually still good if it hasn't formed huge chunks or you can crush it back into small enough bits. Most everything else will last a good long time as long as it doesn't freeze or get left in the sun for an extended period.