Years ago, I remember there being a formula for tank water changes...
For example if you change 20% of your 100 gallon tank every two-three days after 5 water changes over 10 to 15 days you will not have entirely changed and/or rotated all of the older water out of your tank. It would only be 68% or so...
There was a formula that would allow one to determine the number of water changes at a specific percentage required to nearly (closely) cycle the entire tank. Of course within reason as one may be stuck at 99.9% for a long while.
For example if you change 20% of your 100 gallon tank every two-three days after 5 water changes over 10 to 15 days you will not have entirely changed and/or rotated all of the older water out of your tank. It would only be 68% or so...
There was a formula that would allow one to determine the number of water changes at a specific percentage required to nearly (closely) cycle the entire tank. Of course within reason as one may be stuck at 99.9% for a long while.