I would say that they need more than 20 gallons. They really grow huge and produce an incredible amount of waste. 40 gallons for one fish and 20 more for each additional fish sounds more like it. Believe me, I'm not exaggerating. big tanks for big fish, eh
?
heres a picture:
http://www.ifs.tas.gov.au/fact_sheet...20goldfish.jpg
more info about goldfish:
http://www.fishbase.org/summary/spec...ary.cfm?id=271