Make sure that in addition to your pellets, you feed some form of roughage, and veggies. I use FD gammarus for the roughage and protein, and peas or cukes for veggies. I've gotten a one inch fish to hit 3 inches in a month and a half by doing this.
Like everyone else said, frequent water changes, and HEAVY filtration. If you can go double, you'll be good. Besides, goldies LOVE to play in the current from the filter!!