Originally Posted by finnfinnfriend
I thought if you make too big of a water change it can mess with the cycling process or an established cycle. Is that not true?
No that is not true. Water changes have no bearing on the cycle - the bacteria lives on the surfaces in the tank and filter, not in the water itself. You can change as much water as you wish, so long as the chemistry isn't too different.
While you are in the process of a fishless cycle, water changes are not as important. The bacteria can grow in ammonia concentrations that are lethal for fish. During a fishless cycle there is a time when a water change may be needed, and that's after the ammonia has been converted to nitrite. If the nitrite concentration is too high, it will cause the cycle process to stall.
During a fish in cycle, the goal should be to keep the ammonia level as low as possible so that the fish is not poisoned, so large frequent water changes are needed.