In the past I've used mostly Botanicare products for my grows. For my current grow I placed an online order for more of the same but the dealer made a mistake and shipped me Bio Bizz products...Bio Grow, Bio Bloom and Alga Mic instead. Rather than return these I decided to make use of them. Now...
It's only 4 weeks into flower. You should prolly just be patient and give it time. Buds won't turn sizable until the last week or two, when the calyxes start to swell. Bud size is also genetic.
Might want to consider getting a larger watt light for the future also.