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Pay particular attention to the checklist and the bimac care sheet. Both of those say 50 gallons is the minimum size for a bimac... lately we've been saying 55 gallons more often, since that seems to be a standard tank size but 50-75 gallons is the tank size range.
Also, these sorts of questions are best posted in the "octopus care" or "tank talk" forums, since "marketplace" is more for buying an selling things. But please try to look for answers to your questions in the articles before asking... the experts have put a lot of effort into writing up the information as well as they can in the articles, so it's likely you can find the answers to most basic questions there, and if they have to re-type it every time someone asks, they're far more likely to make a mistake, and they have less time to answer the questions that aren't in the articles.