What are the other readings on your tap. Does it have any chlorine, chloramine, ammonia? Have you tried using an airstone. Might not be good for the plants but help the fish. I personally have an airstone for aesthetics, and my plants are doing fine. I'm not sure this is an answer, but may help. just my 2c
Has you water dept recently done anything different? That may cause a change in what you add to the tank.
Has you water dept recently done anything different? That may cause a change in what you add to the tank.