First ecosphere!

Hello, today I decided to make an ecosphere from the pond in the backyard. (This is the first time I do something like this) After doing a bit of research, I saw that there should be approx 25% soil, 50% water and 25% air. I added two types of algae that were in the pond, one deep in the water and the other type that was sitting on the surface. There is one problem, however. This pond is man made and it doesn't have any soil, just dead leaves in the bottom and such, so I decided to replace the 25% of soil with it. However, after doing some further reading i found that it is not recommended to have so many biological waste inside,since the organisms in it could not process it on time, which could lead to decompositionand the dying of the system. I managed to catch 3 snails and many other little organisms such as worms. My questions are: 1. Should I replace the dead leaves for some real soil or should I let it be? 2. Should i leave the lid open for a few days or just keep it closed (i am afraid my snails will escape). Any other tips are welcome!! I really want to keep the tree fella snails alive!