After reading the forums on different topics, I too have been wondering about a canister. I'm familiar with the old school under gravel (which seem to be going the way of dinosaurs), and HOB style because I've used one on a 20g for 15 or so years. (2 different brands because the first just up and stopped working one day.) I recently bought a submersible for the 25g community I set up for my sister, and while it's absolutely silent, it's obvious in the corner of the tank and created a pretty strong current.
How do canisters do with power outages? Some HOBs absolutely must be primed again after losing power, which can be a nightmare if it happens while you are out - or on vacation.
How quiet/noisy are canisters? Can one be set up to handle multiple tanks? Is it best to have just a canister, or should it be supplemented with a backup? And do you have to unplug a canister to do water changes?
I'm planning on doing a heavily planted 29g for my gambusia, but I'm also looking at a large tank (180g or so) for my sea monsters (large tinfoil barb and Denison barbs). I want something that's going to effectively filter the tank without too much hassle. Skippy (the tinfoil) is large, a decent waste producer, and rather destructive because he races around and crashes into stuff. (He's broken 2 glass thermometers and a couple heaters already.)
Sorry for the potential thread-jack, Owens. You brought up a topic I've been mulling over, so rather than starting a new one, I thought it might be better to ask here.
Oh, about your bala sharks.... My tinfoil is in the same family. They need a LOT of room. I'd seriously look at getting a very sturdy tank with a heavy lid because they will crash around, especially if startled. My tinfoil absolutely HATES me working in or cleaning the tank. Freaks him out something fierce, and last time he got so stressed he jumped over the aquarium support that keeps the top from bowing. I got a face full of tank water for my efforts, but at least mini Shamu stayed in the tank. (And for those who picked it up.... Yes, single tinfoil. Lone survivor of a difficult to find color strain. Would love more if I can find them.)