You don't really need to use any of the old water. The important thing is that the old water and new water are the same temp. and of similar ph, hardness etc...
What I usually do is a larger than normal water change the days before the move (I routinely do 50% per week). I would do my normal 50% water change, then 3 days later another of say 60-70%, and then the day after that, move them to the new tank with new water. This way you minimize the change in water parameters.
Of course use your cycled filters to prevent any ammonia or nitrite spikes.
Burt
What I usually do is a larger than normal water change the days before the move (I routinely do 50% per week). I would do my normal 50% water change, then 3 days later another of say 60-70%, and then the day after that, move them to the new tank with new water. This way you minimize the change in water parameters.
Of course use your cycled filters to prevent any ammonia or nitrite spikes.
Burt
