i have a kanger subtank mini with a laisimo 200w box. I'm currently using .5 ohm coils and vaping "milk" by glas. I keep my box between 25-30w all the time. My coils are burning out in 2-3days. I always keep the airflow all the way open as well. How could I possibly be going through coils this much?
Air flow is both your friend and enemy. Although I am not familiar with the Kanger Subtank Mini, generally speaking, MANY atomizers rely on air flow to cool the coils AND pull more e-liquid into the wick. When you draw on the atomizer, you create a partial vacuum in the chamber which allows more e-liquid to be drawn into the coil area than natural wicking action would on its own.
Also, you didn't state how much e-liquid you were going through in a day, but depending on the composition of the e-liquid, I've personally had to re-wick from between 10 and 40 (or so) ml, depending on the e-liquid being vaped.
As has been stated above by DebiK, dark or sweet liquids do gunk up coils faster. Two or three days on a factory coil isn't that unheard of.