Aquasoil buffering and plant deficiency

Hello, I use RO water in my high tech iwagumi and use seachem alkaline buffer to raise the kh to about 3 and my gh to about 6 or 7 during water changes. After the water change, almost immediately my water buffers down to 0kh and 4 gh no matter what I do. I wouldn't be worried because I have a really healthy tank otherwise and EI dose, but my ammania bonsai has started rotting away and idk what to do. I think it might be a deficiency due to such a low gh. Any help would be awesome, thank you.

Also, I forgot to mention I use seachem equilibrium to demineralize my RO