Yes they do eat real plants.For adult fancys I'd recomend 100 litres to start with and then an extra 40 litres per fish.Normal goldfish get huge and therefore they should only be kept in very large tanks or ponds.
Does this look any good? I'd be running it in conjunction with slicker pads and 1-2 cold water changes a day.
http://www.trademe.co.nz/pets-animals/f ... 081968.htm