i use promix but i doctor my promix with coffee grounds, baked ground eggshells, tea leaves, fine sand, ground dried kelp and dried chopped algae from my fishtank, now you don't have to go to this extreme. i am experimenting with a few things this year. when i start to move the plants outdoors in june, i will give them a drink of fish fertilizer.
last year when i started using promix on my potted up plants, the first thing i noticed is how fast the water drains out of my containers. as fast as i poured the water, it would stream out the bottom of the 1 gallon containers. on future pot ups, i put a couple of rocks on the bottom of the container and cut out a circular piece of cardboard, then added the promix. this help retain some of the moisture but eventually the cardboard dissolves. now, i purchase coir containers, put my potted up plants in it first, then move the plant into its container surrounded with promix. by using the coir containers first and not plastic, i can monitor how the roots are evolving. when watering i sometimes have to wrap the coir container to prevent it from buckling. i got the idea watching my dwc plants in rockwool and how i could visibly see the roots piercing through the rockwool working their way to the bubbling oxygenated nutrient mix.
this year, i have also started using aspirin water, given to transplants that appear to be in shock.(325gram tablet in 1 quart of water-then soil water, i tried to foliar spray but i think my tablets are coated and that left a residue on some leaves. it work wonders on 2 hot lemons that i moved from dwc to soil and on a yellow 7 that didn't like its move when potted up - that was before i moved to coir containers.
(this guy germinated jan 9, its a bombay morich from pepperlover stock. sorry about the sunlight...ha,look there, if you look on the upper right leaf you can see an aphid; i still keep my soil plants in my germination chamber at night with heater turned on and covered, in the day they are uncovered and no heat)
hope this gives you a few ideas as well.