Goldfish are among the most popular fish kept as pets because they do not require a heated tank, which can dramatically cut down on maintenance and cost. A goldfish tank will require even less maintenance if it is populated with scavenger fish, who eat debris and algae. There are several excellent, hardy and non-aggressive cold water scavengers that can be placed in a goldfish tank. When placing any fish in a cold-water tank, remember to avoid rapid temperature changes, which can send fish into shock.
Chinese Algae Eaters
Chinese algae eaters are frequently sold in pet stores under the generic name "algae eaters." These fish are clear with brown and yellow stripes and grow to be 4 to 5 inches long. They eat algae and decaying matter from both the sides and bottom of the tank, and may even try to eat debris off of other fish. These fish are very friendly and are unlikely to fight with one another or goldfish.
These spotted bottom feeders have a long, snakelike body and whiskers similar to catfish. They are friendly, hardy and typically scavenge for debris at the bottom of aquariums and in gravel. Loaches can grow up to 10 inches, though, so it's important that your tank is a large one if you plan to use these scavengers.
Freshwater shrimp come in a variety of species and colours, but all are suitable for a cold water aquarium. These tiny animals are excellent tank cleaners because they scavenge in gravel for tiny particles that can otherwise cloud the tank. Shrimp should never be larger than your fish or you may have fights, and aggressive fish should not be kept with shrimp.
These small, speckled catfish grow to be about 3 inches, making them an ideal choice for a smaller tank. They dwell primarily at the bottom of the tank, making them a perfect choice to clean up gravel, but will also periodically scavenge along the sides of the tank. The behaviour of these fish can be fascinating to watch. They swim while sweeping their heads from side to side to pick up debris. These fish are docile and should not be kept with aggressive fish.