Hamsters, as are all rodents, are inveterate gnawers. You find that even if you lay on the very best chew toys for them they always want to chew something else. Its important that you put an end to this particular behavior however, not least for his won health, and also for the structure of the tank. The only solution is to buy a nice new plastic small animal habitat for him. These can be bought relatively cheaply and can be the same size and shape as a regular aquarium.