My idea is certainly not original. I don't remember if it was on this forum or another where a fellow reefer has been doing these sorts of water changes. And I am clear on making sure that the new water has similar parameters as the display ( temp, pH, alk, salinity, etc)
My thoughts were that I could diminish nitrates and phosphates through these water changes as per Randy Holmes-Farley: Water Changes in Reef Aquaria
http://reefkeeping.com/issues/2005-10/rhf/index.php. And as I've already said I currently have a skimmer, use occasional GFO in a reactor, I also have a small bag of carbon (the black carbon not bio pellets ), Chaeto.
What I would most like to do is avoid long term accumulation of anything toxic
and avoid depletion of anything essential like a trace element.
I believe I test parameters reasonably regularly but I hate test kits because of their seemingly poor consistency and accuracy. It is difficult to be committed to testing regularly when you are doubtful about the results. And yes I have tried Hanna checkers, Red Sea, Salifert, etc. My favorite test kit is the Hanna alk checker because it does seem accurate and consistent. I only test for alk, mag, ca, salinity, less frequently for nitrates and phosphates. I know there are more test kits for more elements but I am limited by my drive, frustration with current test kits reliability and quite frankly my unwillingness (laziness) in wanting to add a gazillion trace elements
My tank has been up for years with lots of live rock and a deep sand bed.
Changing only five gallons means I don't have to turn off my return or power heads. The only thing I have to turn off during the water change is my ATO. It's fast and reasonably easy, plus it gives me an excuse to stand in front of the tank for a few minutes and observe and enjoy
What I don't know is if there are organisms in the water column that are beneficial,and whether I am removing too much of these with the frequent water changes.