Think of it like putting a bag over your head and recycling the air you breathe, eventually the air becomes contaminated with carbon monoxide and you die from esphixiation. The only way to fix it is with fresh air... Water changes add more than just trace elements, it rejuvenates the entire chemical balance. Everytime you do a water change, youre dilluting harmfull organics. Many people never do water changes and claim to have zero problems.. Its up to you...