A 6 or 7ft tank. I am guess the dimensions will be around 6x2x2?
For large tanks, sumps can be cheaper. For larger tanks you will need multiple canister filter which can start to cost $$. Such as 2 Fx5s would be around $450 w/media if your lucky. BUT, in the long run, 2 Fx5s may be a lot cheaper. @ Fx5s would equal to 10 liters of bio, more mechanical than you would ever need and those to filters together would only consume about 103-105 watts @ 1200 GPH. A Quiet One 6000 pump which are very efficient at pumping with low power consumption, would be around 140 watts to get 1200 GPH at 4 ft head.
The Fx5 I am just using as a example and not trying to steer you to buy it but it is a great filter over all with a high flow rate....again, not trying to talk it up, but no other canister filter has that flow rate and media capacity for the price....really, just using as an example
I really like canisters over sumps due to the fact that they can be less noisy, take 1/3 the space of a sump, cost lots less to run in electricity, can filter mechanically better in some cases and there may be some others but thats enough for now.
You can design a sump to handle almost any size tank you want at any filtration volume and flow volume and perform a variety of different filtration types such as, Mechanical (Stepped PPI), Chemical (Carbon, Phosban, etc.), Biological (Nitrification and Denitrification). You can do the same in a canister but not at nearly the volume extent you can with a sump.
