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I have a Dennerle Scaper's 55l tank which I will be using as an Ancistrus Claro tank. I plan on using a sponge filter as well as a small internal filter as my filtration to work alongside regular water changes.

I will also be planting the tank with mosses and plants which will grow on rocks/wood (anubis etc) and was looking for advice on suitable internal filters which aren't too unsightly and would work well alongside a sponge filter, and not suck in any (hopeful) fry which are spawned.

I have never been a fan of internal filters for several reasons:
1. They tank up tank space. This matters more the smaller a tank is.
2. The are more work to clean than a power filter.
3. They are somewhat ugly inside a tank.

But if you must use one and you expect to have fry in the tank, you may need to use a piece of sponge on the intake to prevent fry getting inside. Why not use a second sponge or a small power filter. The one drawback with sponges/foam filters is using carbon when needed can be a problem, Since I have no internal filters I have no idea how difficult it would be to put carbon in it becomes necessary.

I have a planted tank of similar size with white cloud mountain minnows and I run it with a pair of Hagen AquaClear 100s (20) which have homemade pre-filters on their intake.

when you haul them out to clean you inevitably get water all over the front of the tank and the floor. you can minimize this by using a small pan and putting right up to the tank and transferring the filter to it but you still make a mes IMHE

How about an Aquaclear? They're terrific bang-for-your-buck and easy to clean. Plus you get the added bonus that it adds total water volume to your system where the internal filter doesn't. That's something I would value for a setup that size. I have Aquaclears that are decades old and still working like new. One of mine has run for years with only 3 out of 4 impeller blades; I butterfingers it during a filter cleaning and dropped the impeller on the floor. If you are able to run an external filter that's what I would try.

I currently have two sponge filters in my Nano Cube and will definitely use one in the Scaper's tank. I'd just like a little internal for flow and to also help pick up a little more waste in the tank.