Where can I buy frozen food for goldfish?
You will get frozen cubes at petsmart and petco, both places. It would cost anywhere between 2-3$, try to take the best quality. Goldfish has no special preference for frozen food, but try Hikari frozen bloodworms if you can get them.. In terms of feeding, you can just let the food (frozen cube) float and release itself in the water, and the goldfishes will fend them off. Keeping the filtre off during feeding is adviced.
