Water Changes?!

When you have an 18 gallon clone tube what is the way to fill, keep right, the water? with nutes of course included? Do you change it every two weeks? do you keep less than 18 gallons in it? Seems like a real hassle to dump and measure 18 gallons every two weeks but maybe some advice from of you experts might help me figure a simple way? Thanks...

Im guessing your DWC. If you feel like going crazy you could add 5gallons into a water cooler jug, and do that water dish trick for pets. When the water level goes down water is pulled from the 5gallon jug, then keep doing 5 gallons at a time. It would be easier if you had 2 jugs so you could have one made, a few hours prior ot changing, and just swap them over.

Just change the water. You'll feel better about it.