Internal Filters

I have used Eheim filters for years and for this sized tank would recommend either an Eheim Aquaball 180 or an Eheim Biopower 160.

The Aquaballs have several baskets with sponge media and a small box just under the pump that can take a carbon sponge.
The Biopwers have a sponge in the bottom basket, substrat pro in the rest and a small sponge just under the pump. If necessary, one of the baskets could be used for carbon.


I use a very cheap small internal for carbon. I just remove the media that came with the filter and replace it with carbon granules in a mesh bag. This way I don't have to take out any of the proper media to use carbon. And there are a lot of small internals which have only carbon cartridge media; these type would work too, though the cartridges are more expensive to buy than a bag of carbon granules.

I have used these https://www.fishkeeper.co.uk/aqua-range-aqua-internal-200-filter.
I would use a 200 rather than a 100, even in a 100L tank. There is carbon in the middle of the sponge, but I take that out and pop some ceramic media in.
If you get these don't change the cartridge (as suggested by the manufacturer). I have some that are just rinsed in old tank water and have been working well for >2 years.
Pros - these are cheap & cheerful, they work, and are easy to use & clean.
Cons - they are quite "square", and may not be the most aesthetically pleasing internal filter.