To grow land moss in a fish tank, first find some moss outside. It doesn’t matter which type, but I have only experimented with a few types of moss so I don’t know whichever moss won’t work. After you collect the moss get a container or jar with a lid and fill it with some dechlorinate water. Put the moss in the container and shake it to get rid of the dirt. Repeat this until the water is clear. Take the moss out. You can tie or glue it to wood or rock or leave it floating. Then add it to your fish tank or a container with dechlorinated water that has light. Recommend light is at least 6-8 hours of light a day. I use led lights. After a while the moss will start growing upwards and get longer. I’m not sure what effect fertilizer has on moss because I have not seen any difference after using Seachem flourish for a few months. I will update this when I find a fertilizer that changes the growth of the moss.