Things growers swear by that piss me off. In no particular order and positively leaving stuff out:
Neem oil (weak sauce)
Flushing (pre harvest)
Saying hydro quality is inferior
Advocating use of unnecessary additives (fuck AN)
CFL's (just buy weed)
Now, your turn! Let fly :D
Dewpoint. Don't vent warm humid air into a cool attic or at least plan on black mold. That warm air hits the under side of the plywood sheathing and it's like a bathroom mirror and a hot shower..
More isn't always better. ;)
Fuck the 31 bottles with pricey labels.
ALL you need is GH Flora three part, ph down and perhaps calmag. Believe me, I know ;)