You have quite a bit of fish for a cycling tank (and the tank isn't large enough for the sharks as they will grow to a foot long). You should be doing daily water changes to keep the ammonia and nitrite as low as possible. The neon will definitely not make it through at those levels (have you lost any fish). Another thing that makes the levels even worse is the fact that your pH is 7.6. The higher the pH, the more toxic ammonia becomes.
Another potential problem I see is the crawfish. He may eventually kill all of your smaller fish (guppies, neon, possibly corys). When the lights are out at night and the smaller fish are less active, he could possibly grab them with a claw as he trys to find food. I know that is a problem with crabs and blue lobsters.
Edited spelling.