Goldfish in a Trifle Bowl?

I have two fantail goldfish from Walmart, bought about 4 or 5 days ago. They eat Tetra-fin Goldfish flakes, and I plan on adding vegetables and fruit to their diet in the near future. Currently they live in a trifle dish. It has a flat bottom, wider flat top, curved edges, and a little pedestal. Is this a bad enviorment for my fish? I do 100% water changes everyday and they have two plants for hiding... I know a filtered tank 20 gallons for each fish would be better, and I plan on getting that in November as a birthday present, but until then will this work? I want Hades and Alfred to survive! o.O