I use promix HP straight out of the bail also, I use nutes at every watering and was told by AN and lots of other growers that if you dont nute to a 10-15% runoff the soil gets salinated and causes lots of problems. You are supposed to start doing this when your roots are established and at 4...
I am using 3 gallon fabric pots for my autoflowers and I have been using nutes for 4 weeks now. I try to get some runoff (unsucessfully) but it takes 1 and 1/2 gallons to get any runoff! They just started showing signs of salt buildup so i took a drastic measure and flushed them with Flawless...