Why did my fish die?

Question
Hello Chris
My two lionheads have just died within hours of each other.we have a 30ltr filtered tank that has been set up for just over two months.as well as the lionheads we recently added two small (2.5cm) fantails that appear to be fine. in the space of 45mins the fish became almost motionless then began to lose their balance and within no time had died. the water is changed every week and treated as advised. is there a stand out reason for them dying and what can be done to prevent a reoccurrence?
Regards
Neil Morris


Answer
Hi Neil;

The tank is just too small for goldfish I'm afraid. Just for one goldfish to thrive it needs about 40 liters (approx. 10 gallons) all to itself, at minimum. It is a common myth that goldfish can live in small tanks or bowls. They just can't live very long in there, especially fancy varieties. Sometimes you will see fish live for quite a while in tiny tanks but they are barely surviving. They usually die a long slow death of ammonia poisoning and suffocation from low oxygen levels. Goldfish are just very messy guys that get very large so they need plenty of space and good filtration. Also, with the addition of two more, ammonia and nitrite levels probably spiked, causing the death of the weaker two. Fantails tend to be a bit stronger breed of goldfish than lionheads.

Get a much larger tank for your two fantails and make more water changes in the meantime to help them survive. I would say replace 25% of the water at least twice a week. Testing the levels of ammonia and nitrite will let you know when they need it. Any detectable level of ammonia or nitrite calls for a partial water change right away. They should both be "zero" in an established tank. Here is a good web page about goldfish and what they need to be happy and healthy;

http://www.firsttankguide.net/goldfish.php

I hope they do okay...

At Your Service;
Chris Robbins