Hydroton kicks ass. Rockwool is ok but I hate it.
With rocks, flood as deep as you can. Transplant at a depth that puts roots below flood depth but stem should not get wet. The deeper flood inceases root zone / mass and thus yields increase too. You need a phat res tho.
In hydroton I flood...
Levels of 1500 work awesome in DWC with trees.
Each system / medium has it's own sweet spot.
I run very large DWC trees each under 1kW. These need 1500.
I've ran trays and they top out at 1000ppm.
With small plants you can get away with erring on the low side. ;)
https://www.1000bulbs.com/product/95292/GROW-AAPA110L.html?utm_source=SmartFeedGoogleBase&utm_medium=Shopping&utm_term=GROW-AAPA110L&utm_content=Air+Pumps&utm_campaign=SmartFeedGoogleBaseShopping&gclid=CM2ymK7w4cACFSpo7AodSAQAzQ
Feeding up to 6 of these...