Are you using standard Promix? I haven't had problems but I use the Promix BX with mycorize and Biofungicide. Even with the mix I use I'll add a bit of fertilizer and even Agrigel when putting in larger pots. Be careful how you add Miracle Grow. Don't try to mix the water soluble fertilizer directly into media as you probably won't get a good mix and that can result in plant injury.

My problem with using peat-based pro mix to start seeds is that it crusts over on top and the seeds can't break through after they sprout. This year, I put pro mix in the bottom half of the cell and vermiculite around the seed in the top half. That seemed to fix the problem.

Yeah it was standard. I probably should have been fertilizing from the start. I did a tray back in late Jan. for my early Hoop House plants. They started real slow too, but I chalked it up to being too cool and not enough shop lights. Those early plants are jammin' now that they are in production containers with some garden tone. They started flowering over the weekend.