Hello,

This is usually a sign of poor water quality.  The first thing to do is check your water quality.  Most fish stores will test your water for free, or you can test it on your own if you have a test kit.  You will want to test your water for Ammonia, Nitrite, Nitrate and pH.

A 25% water change will help correct a problem with the water quality.  This should be done on a regular basis every two weeks for aquariums 10 gallons or more, and weekly for aquariums less than 10 gallons.  Make sure that you treat the fresh water with AquaSafe to neutralize any harmful chemicals.

Make sure that you are not overfeeding your fish.  When you feed your fish they should eat the food in 2 minutes or less.  You should feed them no more than 2 times per day.  Excess food will release ammonia and nitrites as it decays.

Also make sure that you did not overstock your tank or stock it too quickly.  You should start a new tank with only 1 fish per 10 gallons of water.  Wait about 2 weeks before adding more fish and only add a couple at a time.  Make sure ammonia and nitrite are low each time before adding new fish.  In a fully established tank you should allow 1 gallon of water for every 1 inch of tropical fish.  For goldfish you should allow 3 gallons of water for every 1 inch of fish.  Also make sure that your filter is big enough for your aquarium.


Sincerely,

Tetra Care