Maybe I should clarify my main question. Why can't you just use the chemicals to keep harmful chemicals at 0? I've had one of my fish tanks for 1.5 years, never cycled. I just use de-chlorinator and Quick Start every time I do a partial water change. Water test a couple times a week, and they're always 0.0 ammonia, nitrate, and nitrite. Never any problems with that tank. What would be the reason, regarding the fish' health, that I should've cycled? After 1.5 years with no fish loss, what am I potentially missing from not having cycled the tank?