Can you use clay pebbles in with goldfish?

Pebbles of any kind are bad news in an aquarium containing fish. They provide places for uneaten food and bits of poo and rubbish to hide. These then go rotten and can not be removed without major problems. Most successfull fish keepers have either a bare base (muck is easily seen and removed with a syphon) or they use a fairly fine gravel as a base in which to grow water plants. (Gravel can still be cleaned easily with a syphon).