Just read my inhalers side effect of low potassium. I have never been tested for this any idea why?

Inhalers. It is usually a very transient drop in potassium that improves within an hour. I have never found anyone with a low potassium due to inhalers.
Not worth concern. I take it that you are inhaling a glucocorticoid. Very high systemic doses of a glucocorticoid will lower potassium; the tiny doses you inhale for asthma are unlikely to produce this effect as it will be overriden by your body's ability to cope. The warning is there for the lawyers. And a low potassium would show on routine blood work should you become ill.