Since it is such a small sump, you can just add rubble (bits of live rock - very porous rock) to any area of the sump. I do this in HOB filters for instance. There are also some other medias you can use instead of rubble if you want. I am a bit old school and do not know what they are called off hand. 
Just gives places to populate. If you use any macro algae in the sump, this will grow pods too.
Just gives places to populate. If you use any macro algae in the sump, this will grow pods too.
