Change in Phrag Culture

I've repotted all my Phrags except Grande into a mixture of 4 parts paph mix (fine bark, charcoal, perlite) to 1 part PRO-MIX HP. This mix drains well but retains moisture. The rockwool is too hard to get, and I found it was too chunky and had to fertilize too often. Most importantly, it MOLDED! I've never had a bark mix mold. The Grande will be repotted as soon as I can get more mix.