TPG Blog My UV bulb was still working when I pulled it out for the winter. Do I still need to replace it? | Decorative Ponds & Water Gardens Q & A

A UV bulb is one of your best weapons in the battle against discolored water. When those ultra-fine particles are exposed to the bulb's ultraviolet rays the tiny particles clump together, and those clumps are then removed by your mechanical filtration system.