true, you have to figure the hight of the filter plus the extra height you'll need to lift the cartridge out from the top. a pool filter would probably never be feasible under a tank but it could be placed anywhere else, like behind a false wall, in a closet or even another room (like a basement).
every filter i've seen that breaks in the middle also has a drain at the bottom so you can attach a hose and empty it before you crack it open. if it doesn't have a drain, you could most likely easily add one.
agreed, you would need to add something for bio, although i've heard of people adding matrix inside the tube of the cartridge for bio with good results on ponds.
i don't see how that would be a problem. if it was i guess you'll just have to use an appropriately sized pump.
since you mentioned sand filters, i'd like to add something; sand filters plug up almost daily when used in ponds because the bacteria quickly grow and plug the gaps in the sand. to use a sand filter effectively in a pond you have to frequently clean the sand with some chemical that dissolves the organics off or replace the sand regularly.
yeah but consider the amount of filtration relative to cost.
an ocean clear 340 canister is probably about $150+/- w/ 40 sq ft of filter = $3.75 per sq ft
a pool filter could be had for anywhere from $200 - $1,000 or more (depending on size or sq ft). take for example this pool filter: $280 w/ 120 sq ft = $2.33 per sq ft
and all you have to do is backwash!!!
...in theory
. it sounds good but i'll let someone else be that guinea pig. i'd hate to have to backwash it every day like the sand filters.
