I agree with sen5241b, what is your bio load in the tank (stocking)?
tank sounds very new- incomplete cycle or restarting cycle due to additional stock-need to find root cause!
I do 5 gal wat changes weekly. I usually fill up the bucket, mix salt and pour into the tank. With doing such a small change out of my 55gal tank would it effect my tank as much? Plus I'm having green hair algae issues. Have had the tank 2-3 months