If you are not breeding the goldfish, you want to maintain a consistent temperature of 23 Celsius (74 Fahrenheit). Because goldfish normally live in a fairly bright, cool lake environment, they need some sunlight during the day and darkness at night. If you use an aquarium light, turn it off at night so that your goldfish can rest. A ten-gallon goldfish tank will weigh approximately 100 pounds. A 100-gallon tank weighs about half a ton.
If you are using an undergravel filter, you’ll need to install it prior to adding the gravel. A recommended gravel size is 1/8’’ (3 mm). Goldfish tend to put small gravel in their mouth, so you should avoid smaller gravel sizes.
If you are using a twenty-gallon tank, you’ll need a flow rate of 100-200 gallons per hour. If you have a forty-gallon tank, you’ll need a flow rate of 200-400 gallons per hour. Undergravel filters are only recommended if you’re on a budget or if you’re keeping sharpness sensitive goldfish such as the Bubble Eye. Canister filters are best for large tanks.
At this point, you can make any necessary adjustments to the filtration tubes. For instance, if you have an undergravel filter, you’ll want to make sure the lift tubes are halfway in and halfway out of the water.
Use either an internal or an external aquarium thermometer to measure temperature. If you want to breed your goldfish, keep the temperature at 10 Celsius (50 Fahrenheit) during the winter months. In the spring, raise the temperature to somewhere between 20 Celsius (68 Fahrenheit) and 23 Celsius (74 Fahrenheit) to encourage breeding. Don’t let the temperature go above 30 Celsius (86 Fahrenheit). Your goldfish will get stressed out if the temperature gets that high. Avoid extreme fluctuations in water temperature.
If you have a ten-gallon tank, you’ll be adding ten drops of ammonia. You can get bottled ammonia at the pet store. You can also add fish food and let it decompose in your aquarium, which will add ammonia to the water.
You’ll still need to add ammonia to feed the good bacteria up until the day you add your goldfish.
After you add the one goldfish, you should keep testing the water for nitrates, ammonia, and nitrites. You want low levels of ammonia and nitrites, but some nitrates are fine. You can add the next goldfish after testing the water for two weeks to make sure the tank is cycling properly and there is sufficient water volume in the tank to handle the additional fish.
