I do minimum 200L water change on a 1200L system per month.
When I get new fish, I do small 20L water changes every second day for 5 times. That is to do the bucket treatment. That is 100L.
Cleaning the QT and refilling it completely, that would be another 180L, but normally I do just the "display" or the sump. Not both at the same time.
I got 2*220L drums. Found it easier to mix the salt in one. Drain / pump 200L from the main display into the empty drum. Refill system from the mixed drum. Then I use the 200L old water for water changes on my 220L holding tank and the 90L QT.
Time taken for one 200L water change for main system, then another 100L for holding tank and another 100L for QT tank. Less than an hour for 3 water changes. (Should time myself next time).
From my thread....
Doing a 200L water change - without carrying a single drum...
First switch off the return, then pump out using a Water Blaster 5000L/h
into empty drum.
Full drum is right next to it, Fill empty drum until its water level is the same as the full drum
Remove the pump from the tank and fit it to the other end of the hose, in the full tank
And pump the new salt water back to the display
Thereafter, dump 100L directly out of the holding tank into drain. Fill the holding tank with the old water from the display.
Do the same to the quarantine system. Dumped 100L, OK and I cleaned the bioballs section in the sump, and used the last 100L old display water. To fill up the quarantine again.