nitrite

Can someone please explain to me how nitrites are turned into nitrates and vice versa in the nitrogen cycle? Thanks :)

So I had a very stable set up in my 5 gal Fluval Spec tank for about 4 - 5 months with my Betta. I then added 5 baby neons to the tank (with the intention uparading later). Everything went well for several weeks, then a fungus bloomed and killed the neons. In a panic, I contacted my LFS, but now...

So I had a very stable set up in my 5 gal Fluval Spec tank for about 4 - 5 months with my Betta. I then added 5 baby neons to the tank. I plan(ned) on upgrading to a 20g.... Everything went well for several weeks, then a fungus bloomed and killed the neons. In a panic, I contacted my LFS, but...