Have you seen his reef tanks? A quick clue to see if someone even understands how to keep a reef is to see their tank. If it is amazing, then tell him that you will take his opinions into consideration. If it is not, try to explain to him in more detail the theory around a DSB. You should remind this person either way that reef keeping is not all 100% science, it is some art, and that there are many successful ways to keep a thriving reef aquarium. I have tried it in almost every way possible ( w/d, ug, berlin, jaubert, modified jaubert, dsb, open) One thing that does throw up a flag for me is him saying that he has been keeping reef tanks since the 60's. Reef keeping has not really been around on a large scale basis for very long. I started my first tank in the late eighties. THe understanding for keeping coral was minimal and I struggled alot. Before this time, reef keeping did not really exist in the US. Most people thought that keeping corals alive in capitivity was impossible. It was German aquarists in the early eighties who first showed American aquarists that keeping saltwater fish and corals is possible. Anyway, back to the point. Always remember that this hobby is very opinionated. Probably the one thing that rarely happens, and the one that annoys me the most, is that rarely do people acknowledge that there is more than one way to do something. It is either their way or nothing. Once along time ago, when wet dry filters were first invented, undergravel enthusiasts were crying foul to me. Telling me it wasnt going to work. Same thing happened when I told my local LFS that I was taking out the bio-media and starting a new type of system called Berlin. So it is the same story over and over. Just try to be patient, explain that there are many sides to fishkeeping, and let it be. Learn and succeed, and dont let others tell you a certain way cannot be done. Sorry if that was a little long winded.