I follow feed charts. I get good results. If they say (
botanicare) mix Grow and Bloom, I do so. I have not experimented with custom made 3-part mixes however, I have mostly used
Botanicare PureBlend Pro, and for my hydro garden the feed chart recommended three bottles of them, Grow, Bloom and Soil Bloom. Mixed them exactly like they said, worked fine.
Next time, I ran just Bloom. Worked fine, however I had additive variables.
It comes down to this, most nutrient manufactures are upping the P-K on their bloom mixes but leaving the N slightly lower. Your plant depending on stretch might need a little more N or not. For the most part, you will find that any bloom formula works well for cannabis and should most likely be used at the start of flowering to increase the onset of flowering.
But if you follow the charts you can stay our of trouble. ;)