I recently put a moss wall into my newest tank with a few easy to get items. I took pictures of how I made it. Hope you enjoy and it's helpful to someone. So far the moss is showing new growth and growing well on the entire thing. It was really easy to make and looks extremely nice even before it's filled in. I haven't painted the background of this tank black as I hope the moss will fill in enough to not need it.
Items needed -
Poster Border or Report binders
Plastic mesh or craft cloth
fishing line or cotton thread
Aquatic moss of your choice. I used about a tennis ball sized portion for this 3 gallon.
I cut the plastic mesh - 2 pieces- to the correct size of the tank then cut the poster border to the size of the sides of the mesh. I used the poster border to hold the plastic mesh tightly to the sides of the back of the tank just like you would with dividers in a split betta tank. It sits flush to the back, so there isn't really any room back there except for water to flow through a bit. I also did a piece for the top just for looks and to keep it from bowing since the mesh I used is extremely thin.
I laid one piece of the mesh on a piece of cardboard and then spread the moss I had cut up into small pieces across the entire surface of the mesh, leaving the bottom where it is going into the substrate and the top that will be above the water line clear of moss. It may grow to the top and out of water and looks really pretty but does best if it grows on it's own and isn't put there at the beginning.
I then put the second piece of mesh on top of the first and sandwiched the moss in between the two. I took fishing line so that it won't disintegrate with time and tied the mesh together in several spots to keep it together tightly in the middle and to ensure there is no bowing or curve away from the back wall. I wanted it as straight as possible across the entire thing.
Lastly I slid the sides of the mesh into the borders and it was ready to go into the tank. I should note that getting the borders on this mesh took some time as the mesh is really thin - I wanted it thin so the moss would grow out faster than through a thick mesh. I used a thin piece of cardboard to help slide it through then just carefully removed the cardboard when I had the mesh where I wanted it.