Well I think this is something we have all learned or even knew before getting into the hobby. Unfortunately I wasn't a member of MFK at the time but when I got my 30 tall a few years ago , I would just go to the LFS and ask them what would Be good with what I already have. While most of them were properly informed and knew what they weretalking about, one day I went in to get a pleco not sure what kind but planned to be some small type. They convinced me to buy one labeled as columbian spotted pleco and it was not until I got extremely serious about the hobby that I thought to look up his species info on planetcatfish. Couldn't find anything so looked it up on Google and apparently columbian spotted pleco is just a nickname my LFS gave the fish when it was actually pterygoplichthys gibbiceps. Yeah, then I realized that i had been fooled into buying one of the largest (16-18in.) plecos readily available. Luckily a slow grower. I am about to move him from my 30 to my 75 in a few weeks once the tank is cycled. Then probably wind up getting him a 155 wide or 180. But grown to attached to him to get rid of him. What have we learned today: DONT FEEL STRESSED TO IMPULSE BUY!!!!!!