While a goldfish can survive in a bowl without a filter, setting up your fish in a small fish tank with a filter is better for his health and happiness. It also makes things easier on you since the water will remain cleaner, and the tank will be more attractive.
How goldfish breathe unfiltered water
Some fish need a filter in the tank to aerate the water so that they have oxygen to breathe. They are able to absorb oxygen into their system using gills. Goldfish not only have gills but they also have an organ called the labyrinth organ. Located near the gills, this organ allows the goldfish to swim to the surface and breathe air from the room.
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There are other considerations when keeping goldfish in unfiltered water. Goldfish are considered to be heavy feeders. This means they produce a lot of waste, and ammonia levels can quickly reach toxic levels that can easily cause illness or death.
Goldfish in a bowl
If you opt to keep your goldfish in a bowl without a filter, you will need to take care to maintain the water quality. Change out at least half of the water in the bowl each day. When you change the water, be sure to also clean waste from the substrate at the bottom, wipe the sides of the bowl, and clean the plants and ornaments you keep in the bowl.
Plants will help to keep the water oxygenated and will provide stimulation to keep your goldfish from getting bored. Consider options such as Brazilian elodea, hornwort, and java moss.
Make sure you select a goldfish bowl that is large enough to support your goldfish. Keep in mind that each goldfish can grow more than 12 inches long. If you select a bowl that is tapered at the top, don't fill it all the way. Without a filter, there needs to be plenty of surface area at the top of the waterline so that the goldfish are able to get enough air.
Goldfish bowl filter
Daily cleaning of the fishbowl is time-consuming and still does not provide the healthiest environment for your goldfish. Consider getting a fish tank with a filter for your goldfish. The filter helps to keep the water clean and aerated, but you will still need to clean the tank regularly. Every week, clean the tank and change out between 10 and 25 percent of the water.
Water quality considerations
Regardless of the tank setup you choose, it is important to monitor water quality regularly to ensure your goldfish stay healthy. The water pH should be between 6.5 and 7.5, although goldfish can survive in water with pH levels between 5.0 and 9.0. The water temperature should be between 68 and 75 degrees Fahrenheit.
Also, check ammonia and nitrate levels to make sure they are safe for your fish. Ammonia in the water should not rise above 0.1 parts per million (ppm), and nitrate levels should be less than 50 ppm.
Tap water often contains chemicals that are harmful to goldfish, such as chlorine. Allowing the tap water to sit overnight before adding it to the fishbowl gives the chlorine time to evaporate. Using a water conditioner for goldfish is also a great way to remove harmful chemicals from tap water. Some products have additional benefits, such as removing heavy metals and detoxifying nitrates.