It takes time for the two species of bacteria you need to detoxifiy the ammonia and nitrites to get established. If you think you can just add water and fish and some lava rocks you're sadly mistaken. They don't call it "new tank syndrome" for nothing.
Biological filtration is a must! Without it you're just killing fish.
If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.
