This would be my choice, not much easier to maintain than a good old fashioned sponge filter. I have never had to replace a single impeller on any of mine.
Definitely do an AquaClear on the 20. You shouldn't need an AC110, 50 minimum, 70 would be better if the flow isn't a problem.
I don't really see what you are getting at with the canister = sump issue. They are both good filters with strengths and weaknesses that make them more attractive for certain systems and to certain people. Canisters are easier to get going and are superior at mechanical filtration. Well-designed sumps can be more of a pain to set up, but can offer much more media, more flow, a custom design, and easier maintenance. In my sumps I use K2 tumbling media, so I never have to touch the biomedia, just the foam blocks.
Saying a canister =1/4 sump isn't accurate either. There are a ton of factors that can alter the capacity of either. The type of media used, how much, how well it's maintained, etc. can all make a poor sump nothing compared to a good canister, and vice versa.
I don't really see what you are getting at with the canister = sump issue. They are both good filters with strengths and weaknesses that make them more attractive for certain systems and to certain people. Canisters are easier to get going and are superior at mechanical filtration. Well-designed sumps can be more of a pain to set up, but can offer much more media, more flow, a custom design, and easier maintenance. In my sumps I use K2 tumbling media, so I never have to touch the biomedia, just the foam blocks.
Saying a canister =1/4 sump isn't accurate either. There are a ton of factors that can alter the capacity of either. The type of media used, how much, how well it's maintained, etc. can all make a poor sump nothing compared to a good canister, and vice versa.
