Just did a 40 gallon water change this morning, took about 4 minutes total.
I have one of my dj switches controlling a mag 7 pump in a 55 gallon RO/DI reservoir that feeds a 40 gallon make up tank. Another DJ switch controls a mixing pump and heater in that tank. So I press a switch, add 16 plastic cups off salt while the water is added to the tank and flip the switch for the mixing pump. Let that run overnight.
Plumbed into the system below that tank is another 40 gallon tank, water returning from my frag tank to the sump flows through this tank. However, by closing a valve water can be diverted from the frag tank directly to the sump bypassing this 40 gallon tank. Another bulkhead on the side of this second tank is plumbed directly to my fish room sink. I open that up and drain 40 gallons of water.
Close it, and open the valve from the freshly mixed saltwater tank to this one. Bring it back online by opening the first valve back up and I've done a 40 gallon water change by hitting a few switches and turning a few valves
![Wink ;) ;)](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f609.png)
The only real labor is dumping 16 cups from my salt mix into the top tank. Other than that a few switches and a few valve turns is all it takes.
here's a pic of what it looks like...
The blue barrel is the 55 gallon drum of RO/DI
The top tank on the left is the one containing freshly mixed SW, it's not online with the main system ever.
The one below it the tank that can be isolated, but is normally part of the whole system. You can see the sump, frag tank, and fuge on the right rack too as well as the valve's allowing you to cut the isolatable chamber out of the mix.
Hope that helps.