How do you get rid of Old Tank Syndrome?

Do small, frequent water changes of about 10% every 3-4 days, using a gravel washer to clean the gravel (the vacuum thing). Do this for about 2 weeks, and then do a larger water change of about 20%. It will also help to be running activated carbon during this time. After that, continue with 10% water changes weekly, and your tank will be fine.