I have an idea for a mattenfilter in which the water would travel along the length of the filter media from edge to edge, instead of face to face.
My crudely drawn proposal: https://m.imgur.com/NCwJOsM
Basically the filter media would be sandwiched between the tank glass and a piece of fixed acrylic. A pump would pull water lengthwise through the media and output it into the aquarium side of the acrylic wall.
The purpose of this is to hide the filter as much as possible. Decorative backing would be placed on the acrylic for a natural look. The heater would also be placed in the pump chamber.
The concern is that the filter becomes clogged, as it's exposed surface area is greatly reduced. However, the total surface area (used to harbor good organisms for filtering) remains the same as a traditional mattenfilter design. I'm thinking that as long as the exposed filter edge is kept relatively clear this setup should still filter adequately. A coarse filter media strip could even be placed on the exposed edge to make removal/cleaning the intake easier.
Another concern is that, even with a totally clean filter media, it would still restrict flow into the pump chamber such that the pump moves water at rate faster than what can be pulled through the filter. This would be because the water has a significantly more restrictive barrier to pass through.
Another option is to split the filter media in half and put the pump between them, so it pulls water in lengthways through two filter media edges for half the distance. This would double the exposed surface area.
Looking for other thoughts or opinions on this.