>>344164start a saltwater tank, make sure you can lock it down tight, then keep some damsels or a shrimp alive for a few weeks while you learn about parameters and water chemistry, then get your octopus, as a bonus you can watch him eat the previous inhabitants.
You sure you don't want a sugar glider? or a corgi? fox maybe?
I really want this to work out for you op, but my experiance tells me you won't get very far, I have to handle somebody asking for octos or sea horses every other day, and all I have to do is the following:
"So you want to spend the time and money to set up a saltwater tank?"
"Yes."
"For a pair of seahorses/octopus?"
"Duh what have we been talking about?"
"And in doing so you will not be able to keep any of this in that tank."
*I make a wide sweeping gesture across the 1000s of gallons of saltwater fish in our store*
"Oh, uhmm, how much was that set-up costing?"
"$350 dollars sir in all."
"And not even a Nemo? Really?"
"Yes sir, really."
A pair of seahorses or octopus is no match for Nemo, Dorie, or a Lubbucks Fairy Wrasse.
As a second little side tank sure, but for your first, it doesn't happen often.