An interesting question.
I'm in that position where I answer more questions than I ask, and spend a good portion of my professional life writing for fishkeeping publishers of various types. What I know comes primarily through experience. I've been keeping fish since the late 80s, and at certain points have been lucky enough to look after some very big tanks and some very interesting fish. So I'd say that about 90% of what I write comes from that, from my own experiences or those of other aquarists I know personally and can trust.
But there are (many) situations when I don't know the answers to something, and I fall back on a books or web sites. I have about sixty books on fish in the bookcase behind me, though there are really only about ten I use regularly. The first two Baensch atlas volumes are essential for freshwater stuff, Bob Fenner's Conscientious Aquarist for general marine fishkeeping, Loiselle's Cichlid Aquarium for general cichlid topics, for example. I do use web sites, but mostly to cross-check my own opinions or experience on things. There are only a few web sites I'd trust as highly as my favourite books. The Krib archives for example tend to contain some very well argued mailing list posts, and for some topics, like water chemistry, they're well worth reading. At the top end of sites specifically on fish are things like the OPEFE Research Page, which is mostly about piranhas.
When it comes to forums, this is about the only one I participate in to any great degree. The problem with forums is they often have all kinds of weird politics going on behind them, so the loudest voices aren't always the most informed ones. Another problem with forums is that you really don't have any idea of the experience or competence of the person writing the message. That's harmless enough most of the time, and part of the fun of forums is people educating one another. But if I'm looking for something to confirm or refute a fact I'm going to add to an article, I really want to know I can trust the thing I'm reading. I'm not a snob about this, and have had my mind opened and my beliefs turned around by people positing on forums. But since I'll get it right in the neck if I publish something that turns out to be nonsense, I have to be very careful that what I'm writing is as sure as sure can be!
Cheers, Neale
Just a question, when someone ask about a fish problem or information where do you get it form, your own experience, the internet, books, or other source

To help other people with there problems.