I'm trying to lower my TA. My TA was 120 last night. After putting 40oz into my pool about 18 hours later the TA is still the same. I put 40 more oz in. The Sodium Bisulfate I have was keep in a shed and is probably 2 years old. Should I assume that it is no good. When should I test and be able to see a difference if it is still good.