Could it have been that you was watering too much with Mike's mix? I've been using the Aussie mix which is similiar and due the my conditions which is dry, and it has been working very well. I don't have to water but maybe every 10 days tops. I do keep an eye on my phals daily for any changes though. Also maybe if you reduced the amount of coir and added more charcoal or even some bark to the mix. Everyones conditions are different and even I had to add a little coco husk to mine
