Just for the record and reference... one of my preveg boxes. No recommendation, just what I do:

^^filled till close under net cup. 300-350ppm (including 200ppm tap) Little bit of Cannazym.
Germinated in rockwool, on a bed of clay pebbles:
1 layer of clay pebbles in the net cup:
I normally use Grodan, not this cheap white label shit:

^tip discolored from pebbles.
So I basically sink the tap root in between the pebbles through a bottom hole in the net cup. Haven't broken a single one yet during the process (out of many dozens).
Filled with pebbles (not too many on the sides of the cube). Unfortunately grow shops here haven't discovered neoprene inserts yet...
I've let them stretch a little more than usual by keeping them more than the usual 1 inch from my 3x18watt T
8 tubes (else I got too little space to check the sprayers in the tubes later on).
There's 1 small air stone in it, only bubbles in about 1/6th of the surface. Temps range from 70-80f. Never had probs. Leaves on the right is from the motherplant of P#1A and P#1B in posts above. Has been there for months. If anything, it helps keeps the rez healthy.