Kirkland is OK, but it is a high/mid range food, not a premium grade kibble. It is made by Diamond Pet Foods, the makers of Diamond kibble and also Chicken Soup.
Here's it's ingredient list:
Lamb Meal, Rice Flour, Brown Rice, Chicken Fat Preserved with Mixed Tocopherols (source of Vitamin E), Fish Meal, Egg Product, Beet Pulp,, Brewers Yeast, Dicalcium Phosphate, Potassium Chloride, Sodium Chloride, Choline Chloride, Vitamin E Supplement, Zinc Oxide, Copper Sulphate, Potassium Iodide, Thiamine Mononitrate, Manganese Oxide, Ascorbic Acid, Vitamin A Supplement, Biotin, Calcium Pantothenate, Manganese Sulfate, Sodium Selenite, Pyridoxine Hydrochloride, (Vitamin B6), Vitamin B12 Supplement, Dimethylpyrimidinol Bisulfite (Source of Vitamin K), Riboflavin, Vitamin D Supplement, Folic Acid
Now there's nothing too offensive on there, though personally I wouldn't buy a kibble with any form of flour as the second ingredient. Where there are grains in a dog food, they should be whole grains, not fragments with little nutritional value. And since fat appears on the ingredient list before the second meat source, I don't think you can be confident that there's actually a great deal of meat in the food. It is better that the first two ingredients are meat - and you know, for some premium kibbles, the first four ingredients are meat.
Either way, a dog should not have loose stools all the time and this particular food would not appear to agree with your dog if he has constantly does have loose stools.
If I were in your position, I'd try feeding a food with a higher meat content and less grain. Something like Chicken Soup would probably be a good choice, as would Wellness or Innova. Each of those foods has a high meat content, includes fruits/vegetables, and far less grain (they use whole grains too, rather than fragments). IMO it is unlikely that Nutro would be a better bet than the Kirkland, unless it is the Ultra formula.