I bought four goldfish 4-5 months back. I kept them in a bowl of water, and was daily removing a glass of water and adding a fresh glass of water.

Starting 2-3 months ago, everything was fine. But slowly, one of the fish started getting black spots on outer surface of its body and then died. Then, one by one, the rest of the fish also died.

This also happened when I tried keeping them in aquarium which also had an air pump for oxygen. Can anyone let me know what was the reason that this happened?


  • 1
    It's a common misconception that you can keep goldfish in a glass (see @LunarWatcher's answer below). It's animal torture. Changing a fixed amount of water so often is the base for a lot of distress which can end deadly. What are the water values for ammonia, nitrite and nitrate before changing the water? Commented Apr 28, 2017 at 17:01
  • I didnt kept my fishes in glass instead i was saying that i was daily changing a glass of water from the bowl in which i kept my 3-4 golden fishes. Commented Apr 30, 2017 at 10:50
  • I was intructed to change daily a glass of water from the bowl by the shop owner from where i brought my fishes. Commented Apr 30, 2017 at 10:55
  • 2
    I mean't it's a misconception that you can keep goldfish in a bowl, sorry. Everything said applies to the bowl as well. Commented Apr 30, 2017 at 11:28

3 Answers 3


The result may be ammonia poisoning.

The solution may be to add a filter into your tank, and make sure you don't overpopulate the fish tank either. Don't feed them too much.

Further, each goldfish needs 3 gallons of water per inch of their body length or more.


  • 1
    General rule for goldfish where I work is 10 gallons per goldfish. Just to make sure there is room for growing. Plus, most who buy goldfish are beginner aquarists, so we keep in mind that they might not be feeding the right amount or have the water quality where it should be.
    – NealC
    Commented Apr 29, 2017 at 0:20
  • Yes i am a beginner aquarists. I love to keep fishes in my house. I was planning that will gradually increase the size of aquarium and amount of different fishes, but as my fishes died twice now i want to aquire all the necessary knowledge before again bringing them back. Commented Apr 30, 2017 at 10:54

There might be several reasons for fish to get ill and die. Over feeding might result in toxic substances developing in the water. This often weakens or kills the fish. The fish might also have been infected before you bought them.

You need a water filter to handle the waste from your fish, and the fish tank needs to be cycled before you add fish or other animals to the tank.

"Cycling a tank" means letting bacteria that break down waste grow and multiply so they can keep the water clean. These bacteria convert fish waste to plant food, this is called the nitrogen cycle.


Ammonia could have been the reason, or you could have been using water that wasn't filtered enough in the first place. They also would be way too crowded in a bowl, especially with four.

  • but the shop guy told me that i can keep 4 fishes in bowl, but not more than that. Commented May 10, 2017 at 8:27
  • how big is the bowl?! you need at least a 2 gallon for a smaller species of goldfish because they get big because they are related to carp
    – Monotremes
    Commented May 10, 2017 at 12:16
  • 2
    Don't believe the shopkeepers
    – Diether
    Commented Jun 9, 2017 at 15:02

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