If you choose to add p/k boost, this is the method I use for the liquid nutrient Big Bud by Advanced Nutrients. I believe it’s salt based but derived from organic material.
Ideally, in this setting, it is considered best to use nutrients that are salt derived, as these nutrients will not leave residue in the pipes causing possible buildup. Just something to keep in mind… I have not noticed any buildup or problems with my system’s tubes through this second grow while using it for 2 weeks, but I can imagine it will build up if used again (which I do plan to do). Looking forward to documenting.
Either way, my current method is to add ~1mL of your chosen bloom booster to the reservoir, or to the water with which you will fill your res. Then I let the system add its nutrients and such and I had not noticed any issues.
I suppose I don’t have to remind you that the Grobo already adds its own p/k nutrients but adding a booster will certainly increase yield, just be conservative! A little goes a long way I found. And I believe @Chad_Johnson used Big Bud for 5 weeks of flower on the critical purple.
Lemme find it… I saw it there somewhere.
Just did a water change, so may work on it today 
