What do you mean by underwater filter? An undergravel filter is not recommended - one reason why is that your octo can crawl under it!
But other filters will do the job better. What many of us use is a wet/dry filter in a sump.
I don't know about that brand but I used to have an underwater filter (sorry can't remember what brand as I got rid of the thing as fast as possible) in my cichlid tank....it was a real pain in the neck! It blocked easily and fell off the tank walls every other hour! and I would imagine that an octi would find it a great toy, until the impeller chewed it's arms off.
But like I say I don't know much about the brand you're asking about. I think the wet/dry in a sump is the way to go.
If so, No I would not recommend anything like this, fist off, it does not handle the tank capacity that you would need to have in order to keep a octo. You would most likely be better off with no filter at all and using a lot of LR. Second, you octo would with out a doubt pull this lil thing off the wall and carry it all around until somthing bad happened, pulled the filter's cord out of the wall, messed up you cover becasue the cord was being pulled, ripped the tank of the stand, chopped an arm off there has been a 007 here already so that names taken With octos, you really have to think in the worst case scenrio. Becasue you want to be prepared.
I have one in a 29G tank that I'm keeping clownfish in. I use it because the tank is an eclipse and i lost a piece to the built in wet dry filter in the hood. Its a good piece of a equipment, really convinient it saved me from having to drill my hood to make room for the hang off type filters in the back. But NOT for an octotank. He'll definitly play with it and probly get hurt in the process. Everything in an octo tank should be in the sump. If you dont have a sump your probly going to have problems. As your heater(if you have one), skimmer, and filter will be in the tank, he's definitly going to play with something. If you have a sump and want to put this in it. I guess that might work, but I dunno they seem weaker then normal filters to me.
But I'm an octo noob just setting up my tank right now. I've read alot and this is the general opinion. But you dont have to take everything I saw as fact.
Mine doesnt filter as much as the box said. And its a hassle when I want to change the cartridge.
What are your guys thoughts for bio filtration? I currently have a sump, with a refugium, and an "eheim" 2028. Will this cannister filter be acceptable for biofiltration? All the reefers say dont use them, I would like to have low/no nitrates.... Does anyone use a FBF? I will have a DSB in the refugium, and 2" sand in the tank. Biofiltration is quite a hard topic to figure. Reefers dont seem to use W/D, but some do. Are you only supposed to use LR? So many conflicting options.
Oh im so excited, just got the pump for my sump return, 2000gph!!!, for my lil 300L tank it will be awesome.