Like the use of carbon you will find lots of different views on doing water changes. My personal view is that water changes are an easy and good thing to do.
One thing about carbon that came up on a different post is that you should actually check your carbon for Phosphate. Here is a quote from steveweast about checking carbon for phosphate. He has an 850 gallon tank that is absolutly increadable.
"The one thing that everyone should do is test your carbon for phosphates!!!! Place a tablespoon of your carbon in a cup of RO water and let it sit overnight. Now test for phosphates ( as well as just RO water without the carbon in it to act as a control)...I use a Sailfert test kit. I was shocked when I did this test on the carbon that I had used for over a year... the phosphate that it was leaching was off the color chart.... so, for a year, i was just dumping phosphate into my tank.... and this, even though the label said "phosphate free"...maybe they meant that they weren't charging extra for the phosphate. I have since changed to Black Diamond which tested zero on the same test...but, I still test every new can of it ...just in case they change something."
By the way here are two links to posts that steveweast has talked about some of his views and ideas.
His ideas on Phosphate and Saltwater tanks...
https://forums.saltwaterfish.com/t/88577/500-gal-reef-converted-to-850gal-reef
Converting his 500 gallon tank to an 850 gallon reef (with lots of GREAT pictures).
https://forums.saltwaterfish.com/t/114406/phosphate-my-take-on-things
