Neptune's years are 164.8 Earth years. Its days are 16 hours and 6.7 minutes long. Although Neptune's days are shorter than our days, its years are still longer than ours.
Most colorants will last in your pond approximately 30 days. You may have to add more pond dye before 30 days if you have execissive rainfall, run-off, a heavy out flow, or evaporation. If your colorant is fading you will visually be able to tell and should add more dye to the water.
Bleach does eventually lose its effectiveness, depending on how long it is stored. When diluted with water, bleach loses it's ability to disinfect after 24 hrs. www.med.cornell.edu/ehs/faq/biological_safety.htm.