Another question for my fellow growers....is promix soil any good?
You'll have to be more specific. Pro-Mix has been known as soilless (HP, or BX under HID). Premier Horticulture has recently begun selling a massive number of products geared toward consumers under the name Pro-Mix name.
Pro-Mix HP is good, but it's not soil. If you see how I use it (my sig) I add 20% soil and perlite to get a very light, airy soil. It works very well.
If you're talking about one of the consumer bags, you'll have to refer to a specific one. I would be concerned about it containing nutrients. And, if it's too dense/heavy.