I can't say on exact volume needed, but a properly set up 30g wet/dry sump would be enough. Just make the bio area as big as you can. And yes scrubbies are said to haev more surface area than bio balls. And people still buy balls because of lack of knowledge. IMO ---its the same as people still shelling out all kinds of money on water conditioners instead of buying sodium thiosulfate in bulk. Some people need the reassurance of a pretty package thats says its for aquarium use. And that it works miracles.
