Welcome !! These should help. Outside of good water and lots of food and proper harvest the single most effective thing you can do to get larger BG is to delay the onset of sexual maturity in male BG. You do this by having no or few females and being sure not to harvest the biggest males. This suppresses or delays the need/tendency for other males to divert energy to reproduction and allows that energy to go toward an increases size. Allocation of energy to reproductive functions (e.g., gonadal maturation, gamete production, nesting and spawning activities, and brood defense) negatively affects growth rate and, ultimately, maximum body size.