Originally Posted by kandaila
I didn't want to cut back on the water change I was wondering if taking out 50%, adding water back up, and removing another 50% (all in one go) would be equivilent to doing one 100% change....
Unfortunately, it's not....
The first 50% removes 50% of the original water.
But the second 50% only removes 25% of the original water. (The other 25% of what gets removed is 'new' water.)
So the repetition would give you a 75% water change overall.....
If you wanted to do something like this, two 75%'s would probably work better. The first would change 75% (all old water), the second would change 37% (half old water, half new water).
Actually, something like this (75/75) could be a good solution, if your guys continue to get stressed out about being in cups. Good thinking.