No, I don't think the aquarium background would work well. Get the black craft mesh at a craft store. If you can, get these at your local office supply:
Don't worry, that's just an example, you don't have to buy 50. What you want is the slide grip spine.
Cut the craft mesh to fit the tank, then slide the report spine onto each side edge (the part that will go up against the tank wall). Cut the spine to fit as needed. Check to see if it fits the tank and adjust as necessary. Homemade divider.