I hear ya...
But with goldfish, as I keep, it tends to be better to get out at least half their water at a time because of their bioloads -- still, in addition to the weekly 50%, I normally also do a mid-week 15-gallon exchange just to be sure the water is really getting flushed; I figure half of the 50% change for the mid-week exchange, so half of 30 gallons is 15 gallons...
Ooooohhhhh u have goldfish. Yeah they require more frequent water changes due to the amount of waste they produce.