I have a growing number of orchids in clay pots here in the dry of Colorado. I haven't had the issue but I do run a fan in most places I have clay with the exception of a couple I have in orchidariums. So I agree with Sriram, use the disinfectant, water less often and increase airflow and the problem should be solved. I do like the fact the pots hold water in their pores but I can see the downside if stays too wet. How are your roots?