Goldfish erratic behaviour

Question
I just started keeping goldfish as a pet. After two days running my aquarium, I went to the pet store and asked if I need an ammonia test kit. They asked what size of my tank is and I said it was a starter pack. They told me I don't need it so I bought a fantail goldfish. When I put it into my tank, it seems weak and lost its appetite. I did 20% water changes every day after seeing its conditions (morning and evening). I went to the pet store and ask what might happened and they said that ammonia content in the tank might be high. So I continue partial water changes to keep the ammonia level low. However, it died after four days. So I bring my tank water to the pet store to be tested and they said it's fine and its safe for the fishes. So I bought another two fishes to keep the fishes company. However, one of the fishes died after two days. It behaved hyper-actively once I put it into the tank and start darting around the tank. It shot itself up and then let itself floated back down. After few hours, it sat onto the top of the filter and gasping for air. It became very weak and died. However, the other fish behaved normally and in a perfect condition. I want to know what seems to be the problem. Thank you.

Answer
Hi Aamierra,
  There are a few possible problems. First, keep in mind that many of the goldfish that are sold in pet stores are sick to begin with.  The problem is that they are shipped at very high densities, and transmit diseases very easily. This is why most goldfish die soon after purchase.

  Another possibility is temperature. Goldfish cannot take warm temperatures because they are not a tropical fish. Generally they don't do well once the water gets up above 70oF or so.  What temperature is your tank?

-- Ron C.
  rcoleman@cichlidresearch.com
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