That was an old picture he's in a new tank by himself now
I also have a 20 gallon tank that I have Guppies in that I'm going to move out and put in my larger tank and I want to make the 20 gallon tank just a shrimp tank I have plain blue stone an imitation Coral centerpiece is there any other substrate I should put on top of the stone I've read that people say to put white sand and black diamond blast and dust and all kinds of stuffYou may be able to attach Java Moss to your slate, but I dont think it will work well.
I suggest getting some fragile stone or lava rock to attach java moss to. I find they attach easier.