They suggest about 10 gallons per goldfish, as they like to excrete a lot of
ammonia... If you look at other posts, they also don't recommend gravel, as
the fish will choke on it...
The ammonia & nitrate/'trites should ideally be at 0.... You may consider
getting a larger tank... Some fish stores have old displays they sell cheap...
; ) Best of luck and good on ya.....