At this point, many new growers get impatient and hit the hydro store. The store happily sells them a "bud booster".
They take it home and add it to their grow just before the natural "fatten up" around the 6th or 7th week of flower.
Of course they credit the stupid crap they were sold and tell everyone how well it works. :D
If you get sucked in by that, do yourself a favor. Only add it to half of your plants. Then compare them at harvest. You may learn something of value.
Patience is advised.
They all swell up at the end. :)
That said, beware of too much nitrogen in flower. That will cause small, very dense buds and dark green, (almost blue), fan leaves