Water changes, total volume or just display volume?

[KBlue]

Might be a stupid question, but what do people do for their water change? Are you changing out 10-20% based on total volume (display + sump) or just display volume? Thanks!!

 

[bushdoc]

Total volume.

 

[Dburr1014]

Total
My AWC is doing 1%; 1 gallon per day.
Total system, 100 gallons.

 

[Waters]

Unless you have a huge sump, I always assume the two to be about the same amount anyways. I figure the DT minus displacement from rock evens out with the addition of the additional water from the sump.