To get big onions, focus on growing the green tops, which means nitrogen. If you have large healthy plants, the bulbs will receive plenty of nourishment. No need for so much phosphorus and potassium unless they are deficient, just lots of nitrogen, sunlight, and water.

TomNJ

wcthomas thanks for the advice. I'll ditch the bulb food and focus on the the N. Hoping adding some composted chicken manure is still a good idea.