This may be silly since all of the info is readily available in each section, but why not make one master sticky to help people in the planning/building/buying process. Every section has threads about what to expect for each fish. For the building process, the dimensional requirements are the key bits of information. The daunting task of digging through piles of info of what fish eat, behaviors, etc. just to know what size tank will work is rather discouraging. Especially when one wants to build a community of various kinds or a custom tank where the sizes are up to the the guy digging the hole or drilling the boards.
Here is my proposition, why don't we start a thread in each forum (ex. Catfish, A. cichlids, gar, etc) and have the members, who will most likely have more specialized experience with the fish type in question, of what the minimum dimensions should be. Not gallons, but shortest side footprint and depth. Once a general consensus is made, make a sticky listing the fish by type and size so that people wanting a new kind of fish can get a good start on if it will work, because most pet stores always say it will. Once a person can be sure they have filled the minimum space requirements, they can go above and beyond with no fear.
The thread would not need to include every fish ever sold but instead have what I call "fluffy fish" that for one reason or another cannot be kept in a space fitting for them upon purchase.
An example of the format (and I'm just making some WAGs on facts)
PH,
acidic <<<PH effects respiration as well as many other physiologic processes, active happy fish will be in conditions it was evolved/bred for
...Temperature range,
...Warm <<<Yeah, you'll need a heater if you keep your fish in a cold, damp basement. Unless you live in Tropical zones where that is the regular temp.
...Chilly
...Cold <<<Not gonna be happy outside unless you live in the northern areas.
......Catfish
.......Large cats: RTC... "These typically reach a minimum of 3 feet within 2 years"
.........Shortest footprint size, 6 ft <<<This eliminates the skinny, super long tanks with the same volume of large square tanks because of the minimum size.
.........Minimum Depth, 3 ft <<<This keeps people from building 400 square foot ponds out of a 25x25 foot pond liner from the hardware store that fulfills the footprint but not depth
......Tetras:
.......Large Tetras: Mexican Tetra "Typically max out at 6 inches" "Highly active and require larger footprint"
..........Shortest footprint, 12 inches
..........Minimum depth, 6 inches <<<This effectively solves the 125 gal for a tetra type problem.
.......Small tetras
Other fish, like some cichlids do not need a big footprint for growth but instead for territory, that would be good to include. Don't need a 20 page paper as to why a 4 inch fish needs 4 square feet, just that it does.
People who own RTCs and other large fish are familiar with their physical capabilities. Some fish can easily make a turn in their body length like eels while others have the turning radius of an aircraft carrier. As mentioned earlier, a thumb rule does not fit. Let each group of "experts" set the bar.
Having an easily referenced source of dimensions could help prevent people from cutting corners. Granted this wouldn't be perfect but I think it'd be better.
I've seen and help set up something similar on an automotive forums with common information all in one location. In that case it was comparing models (wheel bases, suspension, ratings, etc.), engines (displacement, bore/stroke, power, fluid requirements) among many other things like common problems and easy fixes. On this fish forum, the fat can be trimmed to necessities. Rather than complain about people being stupid, lets do what we can to help them. Once upon a time everyone here was in the position where they didn't have a clue.