I'm doing it every 30 days to be sure.

If you don't have any more mites, why keep using anything? Or do you have a problem with them getting in on there own? If this were the case, and I had a little time, it would be pretty high on my priority list to remedy. I remember seeing a number of posts about ways to stop mites from getting in. If this is not the case, then the pest strip will kill them forever.