So how much does a auto water change... change?

[RKeenan]

So have a RS300 tank and have an Apex and a DOS unit on it. The DOS unit is in the garage with a 33 gallon Brute and the water taken out goes directly to drain. I have always done about 20 gallon WC's manually every couple of weeks with a lot of hose and a Sicce utility pump. Been wanting to try just doing it with the Apex and save a lot of hassle but since it does a 30 gallon water change over 24hrs... How much of the "old" water is actually getting changed? I am sure there is a mathematical way to calculate that percentage but is wayyy above my education to figure out. So was just curious if anybody had a guess?

 

[cjtabares]

This might help, I know there is a section on continuous wc.

http://reefkeeping.com/issues/2005-10/rhf/index.php#13