Perhaps someone else can shed some light on this situation... No pun intended.
Right on Dapps.
I would change things about your setup. If you are going to full flower and plan on growing a big plant or big plants, I would not use a 5 gal for all of them.
I would switch to several smaller 3-4gal square buckets to fit several and lollipop them to fill out the area of the box in colas.
Lollipoping is kind of like growing a big plant but you remove any growth that won't get light and the plants look like dumdums
If you are staying with that bucket I would grow a mom and then SOG the bucket. SOG would be growing single cola plants. so they don't crowd each other
I am not sure how tall you can get and still stay in the box. but get an HPS 250+watt. Or check out the dual tube that has both hps and mh in one reflector.
If you are for whatever reason trying to avoid an HID lighting system. then you could try to make your own phototron. mount some 12" fluorescents in the corners of the box, brighten it up with minimal heat. Then you could also have different spectrums in opposing corners or duel spectrum in every corner.
And they can do tap water for a couple weeks before they need nutes. When you start them on liquid nutes designed for hydro, step them up slowly, to avoid nute burn.
There is a less loss in yield from slightly under feeding a plant then there is from burning it with nutes, which it is recommended that you flush a plant out when it gets a bad burn. Most of my plants get burnt tips on their leaves but its not enough to slow them down.
Also rock wool at the bottom and hydroton on top to try to prevent algae growth on the rock wool. I am moving away from rock wool personally to no rooting medium and hydroton only. Rock wool changes your ph, they say it doesn't if you do the whole soaking thing, but I still think it does. How ever if your tap water has a low ph it stands to reason that maybe you want to have ph changing rock wool.
Not sure if any of my post will help, I just felt like typing.
