slugs vs snails in freshwater

[goldfish114]

After a rain storm, I found a slug or snail without a shell crawling on the floor so I put it in the freshwater 5 gal. aquarium. Then I found another one and put it in the tank also. There was already a snail in a shell taking care of the algae. The two slugs and the snail seem to like the algae. What will happen to tetra or glofish in the tank? Will the snails mate or compete with each other and eat the fish food that fell on the gravel?

 

[greenwater]

The fish will be fine but the slugs will try and steal the snail's shell at night!