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Some Reasons Not to Use Goldfish to Cycle Your Tank

Tips on Cycling Your New Aquarium

(The First Tank Guide)

I generally don't recommend using goldfish to cycle your fish tank for many reasons. The most prominent reasons that goldfish are generally not a good choice for cycling your aquarium are:

  1. Goldfish have different care requirements than do tropical fish, and if you keep the goldfish healthy, and then try to adjust the tank for your tropical fish, you will stress the filter and will cause the tank to at least partially cycle again - you could even cause the tank to completely cycle again.
  2. If you keep the goldfish in tropical conditions, they will be more susceptible to disease and are likely to leave you with a diseased tank, treating the disease will probably kill the filter and cause the tank to cycle again.
  3. The goldfish people use to cycle a tank are usually feeders. These fish are very poorly cared for by breeders, shippers, wholesalers, and most retailers, and almost always bearing some disease, leaving you with a diseased tank which you have to treat and then cycle again.
  4. And, of course, what are you going to do with the goldfish after you cycle the tank?

This recommendation became common in the 1950s and 1960s when the pet trade and aquarium hobbyists were just beginning to understand the cycling process. Since then much has been learned about how the process actually works, and though using a large number of fish - or especially using a large number of feeder goldfish - to cycle your aquarium had fallen out of favor with educated aquarium experts, humane aquarium enthusiasts, and pet shops that really wanted to provide quality information to their customers and help them through the cycling process by the early 1980s.

I really have no idea why information that has been known to be inaccurate and even cruel to animals is still so widely recommended over three decades since it was known to be bad - or even harmful - information is still so prevalent, but among the uneducated masses it is still prevalent, and even some pet shops that claim to be humane, quality, or expert train their employees to tell customers to cycle their fish tank with a large number of feeder goldfish...

Of course, if you are planning to keep goldfish in the tank, then several of these considerations become moot. For example, if you are planning to keep goldfish, then you know what you are going to do with the goldfish once the tank cycles: you'll keep them. You'll also be using goldfish that you want to keep, not feeder goldfish, so you'll be using healthier, more robust, less disease ridden fish as well, improving your changes of success. and finally, you'll be keeping your goldfish in water conditions appropriate to goldfish.

"I am writing you to let you know I found your site very informative. I am a new aquarium owner and am still learning what to do. You have answered some of my questions. Thanks!!!"
February 7, 2002
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June 11, 2015
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