Ph runoff is too low.

[Seamaiden]

Instead of digging the concrete out to create ditches through which the water would flow, you'd instead build up (the corrugated roofing) to create ridges along which the water would flow. Might not be a very workable idea, just popped into my head.

 

[DeRon1]

4-3-1 is waaaaaaaay too strong! The MAX GH calls for is 3-2-1, so that should tell you something right there.
In veg i use GH 3-2-1 @ half strength plus 1 tsp/gal of MagiCal (technaflora).
Also, try using tap water instead of ro. Don't listen to people who tell you that X amount off ppm tap water is no good or too much hardwater. My Florida tap water runs between 300-420ppm's and I don't ever have issues, NEVER.

nice to know this./ i'm in the Fl