3rd grow-1st with aero

hey all I'm not sure what information to offer so I'll start with my setup

400w hps w/reflector 55k lumen
9 net aero tank with magnetic impellar motor
70-75F water
70-80F air with reasonable movement setup not finished yet
small plants 2-3 inches after a week in the aero
ph 6

Symptom is that the plants are somewhat droopy with some yellow and haven't grown much in the week they've been in the aero

questions

1. Is it a bad thing to leave the pump running constantly with aero? Flooding or drowning possible the net tank drains water away back to res so no serious volume of water ends up covering roots

2. How far should the light be away be right now it's 6" and the plants seem to however around 80F

3. How much fert to use I had the ppm at 1000 till last night when I decided to change out the res for fear it was way too much for such small plants...do plants need really need that much of a difference depending on size I figured the ration of parts to water would stay about the same but from what I've read this isn't the case Since the change I've had only put in 1 teaspoon for 5 gallons which should have it somewhere around 300ppm can't tell if this fixes it as it's only been 12 hours how long should it take to respond? and what ppm's are good at certain heights/sizes if someone has a couple stages with how much to put that would be a big help there is anywhere from 250 - 1500 on the web so it isn't very specific

4. given this setup how fast should I expect them to grow and will they grow slowly at first and get faster cause at about a week in the aero I figured they'd be larger

Thanks in advance for any help you can offer I'm sure I'll have other questions but for now those are the main points...don't hesitate to ask for specifics if you feel you can help I really want the plants to thrive like I've seen from other pics of similar grows