If you see any orange or pink film or mold, or it has an unusual oder, toss it.
Room Temperature Storage: If you plan on baking daily or every few days, leaving your starter on the kitchen counter is fine. Keep an eye on it because the warmer the kitchen, the more active your starter will be. It can double in size quickly, in as little as 5 1/2 hours at 70F! You'll need to feed it more frequently, once or twice a day to keep it active and strong.
Refrigerator Storage: I bake with my starter about once or twice a week, so I store my starter in the refrigerator until I'm ready to prepare for mixing dough. If your starter is sluggish after refrigerating it for a while, you can feed it up to twice a day until it's bubbly, elastic, doubles in size and has a pleasant sweet/sour smell.