I think the biggest things for keeping fancy goldfish healthy are HUGE weekly water changes (75-80%) and a ton of filtration.
With goldfish, I don't think anything less than a 75% weekly (if not more often) water change is advisable.
For filtration, if you've got about a 30 gallon tank, two HOB's that can each handle 60g would be my advice and along the lines of what I have in place for our goldfish (in terms of filter rating compared to tank size).
Good luck with your remaining goldies.