Excel is not going to change the drop checker as far as I know, it's not a source of CO2, but rather, a source of carbon...
CO2 causes the ph to drop because:
Carbon dioxide dissolves in water to form carbonic acid, H2CO3: CO2 + H2O --> H2CO3
Then, this acid reacts to form H3O+ (hydronium cation) which is acidic and bicarbonate HCO3- like this:
H2CO3 + H2O --> HCO3- + H3O+
Excel, as far as I know is ph neutral and is just glutaraldehyde...
What are your other specs?