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Fish mentor
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Salt Lake City, UT
Scientific name: Carassius auratus auratus
Max size: 18 inches
Tank size: Depends on the variety, 40-75 US gallons

Goldfish like to have some salt in their water. They are also a very messy fish and they require a lot of filtration. There are many varieties of goldfish. Usually, fantail goldfish shouldn't be kept with common or comet goldfish in a pond because the comets or commons won't let the fantails or more fancy varieties get food. Just beware that goldfish need LARGE tanks and they can't be kept in bowls.

If they are kept in bowls they will stunt. That means that their scales will stop growing due to poor water quality and too small of a tank, but the organs of the goldfish will keep growing because the goldfish isn't yet mature. This will destroy the vital organs of the goldfish and kill it. I have personally seen 16"+ goldfish. I keep my comet goldfish in a 1500 gallon pond. It is a myth that fish will only grow to the size of the tank, Well they will, but it will kill them.

Another problem with keeping a goldfish in too small of a tank is ammonia poisoning. Fish, especially goldfish and koi produce ammonia. Some of it comes from their poop, but most of it comes out of their gills while respirating. If a goldfish is put into a tank with an uncycled filter, the ammonia will build up VERY quickly and then burn and poison the fish. Ammonia poising can quickly kill a fish. That is why it is important to have a cycled bio-filter.

A typical HOB (hang on back) filter typically has 3 types of filtration. Mechanical, chemical and biological. Mechanical filtration filters out all of the physical debris such as uneaten food. It is usually sponge or polyester batting, commonly referred to as filter floss. Chemical filtration is typically your activated carbon or Seachem Purigen. It filters out chemicals such as ammonia, nitrites and nitrates. Biological filtration is usually a ceramic media, a fluidized media such as Kaldnes, or plastic bio-balls. The bio media with the most surface area for nitrifying bacteria to colonize is the best. The nitrifying bacteria breaks down the ammonia into nitrites and then into nitrate and the nitrate is the least toxic and that is removed by your water changes.

Contrary to popular belief, flakes are not the best food for goldfish. My favorite to use is sinking pellets. Flakes and floating pellets cause goldfish to gulp air from the surface of the tank, and that can lead to buoyancy issues. Hikari food is my favorite brand and I feed it to my lionheads.

Goldfish really shouldn't be mixed with tropical fish. Goldfish are a type of carp and they are coldwater. I like to keep my goldfish tanks around 65-70 degrees fahrenheit and I do not use a heater. Goldfish are overall a very hardy fish and will do fine in a pond, even if there is a sheet of ice over it. The KH should be kept between 80 and 200 PPM.
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