Ditto what DoogieTony said. I usually re-wick mine either when I'm changing from one type of flavor to another (fruit to bakery, for example), or when it just starts to taste funky. If re-wicking doesn't help, I build a new coil. If it's not performing as well as it should, I rebuild. Sometimes a coil and wick will last me several days, sometimes only a few hours (I go through probably 2-4mL a day dripping). That's with cotton at 2.0ohm, though, so with silica YMMV. When in doubt, it doesn't hurt to rebuild.