You will know when the juice you are
vaping tastes like burnt plastic. If you look at your wicks, if it's all brown and gunked up and dark-looking where the wicks connect to the atomizer, it's probably a good time to either clean it or replace it completely. I don't like clearos. I started with them and had three fail on me, back to back, within less than a week.
I got my ViVi Nova yesterday and LOVE it. Although... we'll see how long it's atomizer and wicks go....