Dividers are an essential tool in the fishkeepers arsenal.  Pretty much doubling your tank numbers.

We use dividers in a few our tanks.  By pumping the water through the divider we get a powerful biological filter. You now have a Hamburg Matten Filter (HMF). The blue coloring of Poret was for discus breeding. In trials Discus fry would leave the parents body for the black foam. They instinctively migrate to dark colors.

Keeping fighting fish apart, rearing baby fish or just so you can keep a new species, dividers are essential. The density of the foam you should use depends on the intended use. 

For dividers we suggest that the minimum thickness you go is 50mm or 2". Firstly this gives you the rigidity needed to keep the foam in place without any baffles. This thickness is also the minimum needed for the divider to operate as a biological filter. This thickness will work on tanks 450mm or 15" or less.

If you are looking at dividing a tank around 600mm or 24" wide we recommended the 75mm or 3" thickness. The extra inch will give added stability and allow for a slightly higher flow rate. The higher the flow rate the thicker the foam.

We use the dividers to keep different species of fish in the same aquarium. As the fish grow we are able to move the dividers along without having to catch the fish. We place a plastic tray or flat plate against the sheet we want to move . Applying equals pressure across the entire sheet of foam allows you to move it without gaps forming allowing the fry to sneak through.