Whoa.....
Agreed. Ropefish need space - or will, though, that's not a reason to not consider their addition and the necessary arrangements to be made.
Mine are currently in my "hospital" - which is a temporary, tall 25 Gall (30 X 24 inches?) tank. They've had to work it out in there for about 2 weeks. No problem!
(They're there so I can remove snail infestation from my 55 gall.) They could easily live there for a couple of years! Just change the water. Remember, they arean't like 'normal' fish, in that they would rather coil and slither, than stand erect.
In my (granted, early) experience with them, I couldn't ask for a more engaging, conversational, sweet fish! I'm Sooooo glad I bought a mate for the previous one I had. They're not known to mate in captivety, though that's not a big deal, and I'm glad! They need to have another (regardless of sex) to 'curl' with.
Point being, they really are 'cat-like' in their magnetism. Anybody who has a ropefish would back me up.
Not trying to suggest you do something you'll regret (or they), but for what it's worth, if they caught your eye at the LFS, I guarantee, you'll be highly entertained and amused with these guys. Yes, they will eat "small" fish (fry - but which ones don't?) and I even found my two guys curled up in the "Fry Basket" which contained newborn swordtails. MOST of the fry were still flipping around the next morning. (Sneaky little devils). Ropes go with smell, not sight. Neons, dianos, and probably guppies, should be just fine!
They are NOT aggressive. They just look that way!
Again, I'd never suggest an investment in aquaria (or any animal) that couldn't be properly looked after, but more, to inform you of the 'cool' nature of these fish. IF you think you're into it for the long run, then consider Ropefish!
PS - Apparently the can crawl out of the tank - though mine haven't. 1 year now.
back to you...