I very recently had 1 massive mistake with my fishtank. It was not buying a good filter but the all-in-1 hood for my 29. The filter tube was too long but I never noticed until my brother nudged the tank and the filter started spewing water out. whats worse was that I was away and he simply put the fish in a bucket to keep them alive. I came home to only 1 jewel cichlid still alive. I plan on completely renovating the tank once our home renovation is finished. I should have noticed this earlier given that the lightbulbs failed after a month and my filter clogged.