I'm still new to this forum, but I thought I would try and start a discussion about nano tank filtration.
First, in my experience there are 3 main types of filters: internal, hang-on-back (HOB), and canister.
I have used a small internal called the Duetto DJ50. It is either by Marineland or Aquarium Systems. The really nice thing about this filter is that it has an airline in before the impeller. I use this airline for a CO2 disfuser. It also has a pre-filter sponge, this is easy to clean and keeps the biological sponge much cleaner.
I have used HOB filters for 10 gallon tanks since they are so easy to maintain. My big complaint about this type is the extra surface aggitation.
Finally, I'd love to find a small canister for nano tanks, but I think I'd have to build my own. I think a canister is ideal, nano tanks are so small, any filter is distracting. A canister can be hidden out of sight.
So what are your thoughts and favorites?