Is the grain free feed dry or wet? Grain free isn't actually what is best. Low carb is what is best, although grain free is a good start, since cats don't really need wheat. But they don't need corn, or soy, or potatoes, or that type of thing either. However, your question was about hairballs, not food.Brushing, cat lax
He eats all grain free food so his diet isn't the issue.
He vomits a hairball at least one a week.
This season about two a week .
What probiotics do you use?