the single biggest change in reefing in the past 40 years, what would it be??
and
I think DSBs. I don't think that is a good thing but I think most people run one.
Oh, and computers. Also a lot of bad things happened because of computers because I think there is way too much bad information with a relatively small amount of good information.
I think when books were around (they are small things made of paper) the information was better because the person writing the book usually had some experience or they would not publish the book. That takes a lot of time and money.
Anyone can post on the internet and it is immediately read all over the world, then parts of it are taken out of context and rumors start, rumors that are hard to quell and they persist forever because there is no authority to dispute them. There are no experts in this "hobby" because it's a "hobby" There is no school for it and no degrees. A degree in marine biology does not help and may actually hurt. These animals do not act the same in a tank as they do in the sea and the composition of tank water is also not the same as the sea which takes care of itself.
Scientific studies also do not help much because scientific study is controlled by money so studies are short lived, a few months usually. Any tank should look great and be healthy for a few months even if you don't do anything or even change the water.
Experience is the only good teacher in any hobby. We still must of course read, I am a reading fanatic but we need a lot of common sense. If someone has a tank full of hair algae and someone says a sea hare ate all the algae overnight, that needs a closer look. The fact that hair algae disappears on it's own most of the time causes all of these algae "cure" rumors. People are adament that this or that cures ich or algae. Both of those "natural" things usually leave on their own. Ich is a different problem but there are all sorts of "cures" My favorite is cleaner shrimp.
The ich (if it was ich) left on it's own, the shrimp had nothing to do with it but you will never convince people of that so I gave up. After I am also not an expert, just an electrician with a fish tank.