No, sorry, it's not my tank; I don't keep goldies any more (except in my mum's pond)
I would want a 48" x 15" x 18" tank for three goldies.
Honestly; if you haven't got the space for a larger tank, take the goldies back, buy a heater and get some tropical fish; you could have a lovely male betta (Siamese fighting fish) plus a few rasboras and some freshwater shrimp in a tank your size
Tropical fish are not more difficult or expensive. As an example, I've got a key meter that tells me how much money's worth of electric I'm using. I was out for an hour the other day and I'd used 8p; and that was with 5 tanks; three 4 footers and two 2 footers, plus my son had the TV, his PS3 and the stereo going.
If your tank is in a warm-ish room you'll be using literally pence a week.
I have a alot space for a 120L tank, pretty much anywhere in the house it could go. Finding a sturdy strong surface so the cats can't reach up might be a problem. I'll need to talk to my parents when I get the chance..
I'll probably come back onto this forum and ask for info on what's the best colourful fish, that get on with eachother and not fight.
Can a waterfall filter still be used for tropical fish? Stupid question but just making sure.