Clearomizers are disposable and, although not all clearomizer tanks need replacing, the non-disposable tanks still require the atomizers to be replaced regularly.
Depending on your usage, a clearomizer or atomizer can last 2-3 weeks. You'll notice at around the 2-week mark, your e-cigarette will produce less vapour, and it will be harder to inhale. This means it's time to replace your clearomizer with a new one.
When you're connecting your clearomizer to your battery, don't over-screw or over-tighten it. This might damage the seals.