old tank syndrome

I have a 20 gallon, it is old and either the nitrates or nitrites are high ( I forget which is which.) I was wondering if there was a way to refurbish it without replacing water?

here is an article about Old Tank Syndrome. would anybody like to talk about what could be wrong with this article? G~

Here's the scenario: I tried to keep a BTA too soon (should have listened to TDWyatt). My tank was only 6 months old. Parameters were great. Have an A. Ocellaris that I thought would like a host nem. Nem was doing well for awhile, feeding well (although the clown likes the corner of the tank...