I use Canna nutes with great success. It is a complete formula though.
They need A+B, Rhitozonic, Cannazym and when applicable PK. If you stick to Canna's reccomended recipe and feed schedule you should be just fine.
I use it as soon as I see small buds develop and stop as soon as they are developed and fattening up.
You can use Cannas nutrient schedule calculator and grow guides as well.