Mike,
Here is the article that I was looking for:
http://reefkeeping.com/issues/2005-10/rhf/index.php#12
And to summarize RHF (located at the bottom of the page)
Continuous water changes: Continuous water changes, despite their name, are not necessarily performed every minute of every day. The distinguishing feature of these changes is that water is added at the same time that it is removed. The actual rate of addition can be high or low. Reef aquarists (myself included) most often perform these types of water changes with two matched pumps, one that removes the old water and one that adds the new water. Often these pumps are part of the same mechanism (such as two sets of tubing on a peristaltic pump or two heads on a diaphragm pump), but that is not a requirement. I use a dual head diaphragm pump capable of a maximum of 30 gallons per day for each head (a Reef Filler pump from Champion Lighting). In my setup, once I have a 44-gallon trash can full of new salt water, all I do to perform a 44 gallon or smaller water change is plug in the pump. The wastewater is sent down the drain. Sometimes I change 44 gallons in one shot, taking about a day and a half. Sometimes I pump for a few hours at a time, and then wait for a few days.
These changes are slightly less efficient than single batch water changes of the same total volume. A continuous water change of 30% exactly matches one batch 26% water change. As with very small batch water changes, these have the advantage of neither stressing the organisms (assuming the change is done reasonably slowly), nor altering the water level in the aquarium. The ease of doing such changes automatically also makes it far more likely that busy or lazy aquarists will actually do them.