I can give you an example of what I usually run in my very basic of hydroponic systems.
5 gal buckets with 6" netpots grown in Hydroton.
Constant feed drip ring system (when lights are on).
For VEG:
I use "Grow Big" Hydroponic by FoxFarm approx 2 ml per gallon
1 ml per gallon of "CaliMagic" cal/mag solution by General Hydroponics
1 ml per gallon of 'Ginormous" by Humboldt Nutrients
Ph'd water @ 5.4-5.6 (with anticipation of some ph rise before next res topoff)
For PREFLOWER:
I use "Grow Big" Hydroponic by FoxFarm approx 2 ml per gallon
1 ml per gallon of "CaliMagic" cal/mag solution by General Hydroponics
2 ml per gallon of 'Ginormous" by Humboldt Nutrients
Ph'd water @ 5.4-5.6 (with anticipation of some ph rise before next res topoff/change)
For FLOWER:
I use "Grow Big" Hydroponic by FoxFarm approx 1 ml per gallon
1 ml per gallon of "CaliMagic" cal/mag solution by General Hydroponics
3 ml per gallon of 'Ginormous" by Humboldt Nutrients
Ph'd water @ 5.4-5.6 (with anticipation of some ph rise before next res topoff/change)
2 weeks prior to harvest cut all nutes in half.
Last week of flower-run just straight water.
Very simple and very cost effective with great results. With hydro, a little does a lot. My ppm's rarely ever exceed 500-ish.
As for res changes, some do them and some dont.
I'll do a complete changeout from veg to flower.
I just top off with nuted solution for whatever photoperiod it is in, then add water to dilute on my last 2 weeks of flower then complete changeout to just water on the last week.
May not work for everyone, but it works perfect for me.