Keeping an octopus isn't as hard as most articles make it sound. I've successfully kept 2 diffrent species, a Bimac and a dwarf that even an expert in England couldn't identify. By "successfully" I mean from capture/birth to the natural end of their lives. Both were females and both laid their eggs and passed away. Routine water changes, an oversized skimmer, and an oversized filter is all you really need. As far as sealing the tank its a cheap and easy thing to do. Take a piece of "eggcrate", trim it to fit the tank. Take a fiberglass screen repair kit and wrap the eggcrate with it, ziptie it to the eggcrate. The screens openings are way too small for the octopus to to fit through AND it also cuts down on the lighting (they're not fond of bright lighting). If you have any other questions I'de be more than happy to help you where I can.