I agree with koimaiden on the basic fish knowledge. Some people just don't get things very clearly though. As a professional in animals, no matter the kind, they should look at the dirty water and clearly be able to see that "huh that's not good". Some people don't. The best you can do is try to explain things to them. Some people won't listen, but at least others might.
Our soup kitchen, Martha's Table, has a 15-20gal tank. It's filled with green water, and these huge, convict cichlids, some other random fish, couldn't even see them but they don't belong in that small tank. I decided that after my exams when I start going there again, I'm gonna offer to rehome the fish and buy her new, better suited ones, or at least clean it out. She's a nice lady, she prolly doesn't have time, or know better, and knowing her someone prolly dumped the tank on her. ^^ so yay, volunteering to save fishies!