Goldfish live in cooler waters and so will not require a heater in most places. Water temperature should be between 50 and 75 degrees F (15-23 decrees C). If the water temperature drops below 50 they will stop eating as their metabolism slows down and they cannot process the food.

This is common in outdoor ponds, and infact goldfish can live outside all year long as long the water does not freeze over. Even at just above freezing the fish will hibernate through the winter. They can also live in much warmer waters, up to 100 degrees F (mid 30's C) but not for a long time, just as long as a normal warm spell in the summer.

pH levels should be between 7 and 8 and although goldfish are freshwater fish they appear healthier in water with small amounts of salt, about 1 tablespoon for every 10 gallons of water. If you choose to add salt be sure not to use table salt since it contains iodine and other bad things for fish. Salt for aquariums can be bought at most pet shops. Other salt you can use if 'rock salt' which is used in water softeners.

Goldfish do grow quite large, about a foot long depending on the type of fish you have. Keeping this in mind it is recommended that you have at least 10 gallons of water for every goldfish you keep. Small feeder fish will quickly grow and require this space before you know it. Bowls are not a good choice for goldfish, even though they are usually called 'goldfish bowls' because of the size the fish become.

Because of their great size goldfish will produce lots of waste. Water changes should be done weekly, exchanging old water for fresh water. Different people recommend different amounts of water changes, usually about 20% a week. By doing these water changes you remove harmful waste chemicals such as ammonia from the water. Even the best filters will miss chemicals which will just make your fish sick.