What type of bark are you using? Aspen is the best in my opinion. A lot of people use cypress mulch too. But I've heard from many places that pine bark is NOT ok to use. Although I have seen what looks to be pine bark in pics posted by well known breeders so I don't no for 100% sure that pine bark is bad. I have never used pine bark, I used to use cypress mulch but now I spend the extra money and use aspen to ensure the best results.