fish always dying

Question
I have had an aquarium for a couple of years and can't seem to keep fish alive for any length of time.  When I check the ph, alkalinity, etc., it is almost always okay.  They often die after I remove 1/4 of the water and clean tank.  How long should I expect fish to live?  It is a freshwater eclipse 12 gal. aquarium.  I see other people with 10 gallon dirty aquariums full of fish and I work hard at ours and can't keep fish alive.  What in the world am I doing wrong?

Answer
Hi J.,
Thanks for your letter. Tropical fish should live at least a couple years. Aquarium care can be frustrating. From what you have described, I will offer a few educated guesses about what could cause the problems.
1. amonia. Did you use any amonia cleaner, such as glass cleaner, to clean
the tank? Any amonia in the water will kill the fish.
2. your water supply. I always recommend using bottled water unless you
have access to a pure water supply. When I lived in Los Angeles a few
years ago they used to enclose a flyer with our water bill that showed
fish floating upside down in an aquarium with a "not" slash across them.
The message was that they add chemicals to the tap water that kill fish.
3. over feeding. With new fish, only feed them one flake or one pellet per
fish per day. If you feed more than that, they will get sick and die.
Usually it takes longer than you describe.
4. bad stock. If the aquarium supply shop has any of the above problems,
then the fish could have been half dead before you got them.
So, I recommend that you try again, but follow the instructions for easy
aquarium care posted at my site:
http://steamboats.com/aquarium.html
My system revolves around using organic biology, "Cycle," or a similar
product to condition the water. This adds friendly bacteria to make your
aquarium more like a natural habitat. Also, avoid over feeding.
Feel free to print out the instructions for future reference.
Write back if you want to discuss further.
I encourage you to try again, once you discover what was causing the
problem.
Sincerely,
Nori