Why does my Ammonia Treatment not work?

Hi. I currently have Two Red and White Ryukin Gold fish, 1 Black Moor, two apple snails, a female crowntailed betta, and two African dwarf frogs in my 10 gallon tank. I also have 6 leaved plant (which I know isn't dying). All of the residents of my tank are babies so they can fit for the meanwhile. Recently, my other Black moor died of Ammonia poisoning. The other one is VERY sick and only stays at the bottom of the tank and the two ryukin are turning black gradually. I have tried to do 15% - 50% water changes while cleaning the gravel and the ammonia is still toxic. It has never been this high a month ago, it's only recently that the Ammonia level became this toxic. I tried using Tetra EasyBalance and Some NutraFin Cycle bacteria but NOTHING IS LOWERING THE AMMONIA! Can someone help me please?!?!?