flowering ?s new to the uc

Hey what's up everybody, im brand new to this uc and just had a few ?s about flowering and if my plants look normal I feel my buds look pretty small for being close to 4 weeks in to flowering. Is this norm or is something wrong? Is there anything else I can add or do to make them grow bigger? Lil info I'm running DB20 site13XL, 8400W, running DM gold flower A&B, cal mag, and BB at the moment my ppm is at 550, ph 5.7 temp 75 Rh 60%. No co2 at the moment.All I kno about the strain is it's purple. And ya I kno purp isn't a very big yielder but that's what my patients are asking for. Excuse my photos i only have a camera phone and no home computer.