The way I'm reading your inital post, it seems youre gonna add this octo tank to the rest of your system, meaning youre going to plumb your reef tank and your octo tank to the same sump. If I'm not mistaken, (and I'll admit I know next to nothing about octos) wouldnt that pose a threat to your reef tank if the octo happens to ink? I think I've read that if one does ink a large water change needs to be done...
From Dr Fosters and Smith "Always approach the Octopus slowly to avoid causing it to release its ink cloud in defense. In the aquarium, this release of ink will necessitate a large water change to avoid its death."
If the ink poses a threat to the octopus, wont it also pose a threat to your reef tank's inhabitants? Again, I apologize if I'm totally off base with this, as I said I know nothing about octos, but I wasnt sure if anyone else caught on to plumbing everything together...