I remember a long time ago someone from this area was trying to do a foam type backdrop and were testing it to see if it affected the water parameters. I'm not sure whatever happened with it all. It's an interesting idea, I remember Aquarium Sales & Service had some foam sections they sold at the store when it was open. It looked like it was painted, although Im not sure how that is done. All materials would have to be non-toxic and not leach back into the water column.