Regret buying a 20 inch jardini the most. He killed everything in the tank.
This was years ago, sights like this to research fish were non existant, and no literature I read warned me what badasses jardinis are. Thought I just had a psycho individual. Since I''ve been here, found out better.
Also regret not buying a 10'x5' glass tank advertised for $500. Now looking at buying a similar size one, and it'll end up costing me close to 10K. Lesson learned...when a monster tank goes for cheap, snap it up! Even if you have no space, or thinks its too big, you'll probaly regret it in the future when your circumstances change.