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An octo tank requires the same water quality as that of a good reef tank...so most of us use protein skimmers...I would splurge on the skimmer, get the best one you can $$ !
On the bright side (pardon the pun, I couldn't resist) you don't need to have halide lights, so just a standard flo. fixture is ok...
Be sure an put your tank in the database when you get it up and running...good luck!
A word about protein skimmers. You see their real value as your octopus grows. As your octo puts out more waste, the skimmer becomes more valuable in keeping your tank clean. And you'll be really greatful to have the skimmer when your octo inks, because it does such a great job of removing the ink from the water.