A lot of problems. How would you change water ? Lots of debris will collect in the bottom center. How to get dead or sick fish out ? Would you want to move the top every time you want access to the tank, change filter media ? Seems like a lot or trouble. Condensation may collect at the glass top hampering your view of the fish anyway. If you have kids, cats or dogs, then all sorts of fur or knick knacks could find their way into the tank and it'd be hard to get them out. Oh yea, internal filter will probably work if you still forge ahead. Good luck.