Tank that Smells

Question
I have a 55-gallon tank with 4 large koi and 2 goldfish with 18 catfish. All of a sudden our tank had a foul smell. Changed almost all the water. Changed filters and washed everything. The smell hasn't gone away. I was wondering what could cause it?

Answer
Hi Darlene;

These are all very messy fish so the tank is just overcrowded. Cut back on food to help a bit and you may want to add more filtration and/or get a larger tank for them.

You may have trouble with toxin levels too since the filters were cleaned at the same time as the large water change. The filter is where the beneficial bacteria lives that consumes the toxins from fish waste. The toxins will make the fish sick. Make a 25% water change at least once a week while vacuuming the gravel. This should help everyone feel better and the smells will hopefully be kept to a minimum while the bacteria balance recovers.

Followups welcome

At Your Service;
Chris Robbins

Come on over and join us on the freshwater fish forum at About.com to get even more information too;
http://freshaquarium.about.com/od/questionsanswers/a/naavigateforum.htm

My member name is ChrisR62. See You There!