Try the TDS or MSDS. Maybe you are lucky. But why don´t you make a calibrating set yourself? E.g. 1. 100% cleaner > measure the refraction index, 95% cleaner + 5% water > measurement and so on.
When you get a reading you can check your table and you are done.
No experience in pig stable ventilation.
Might be that on some point the concentration of you sulfuric acid is so low that fungi or bacteria are let loose on your scrubber. The ammonium sulfate, which is formed in your scrubber is also part of nutrition salts for yeasts. Additional, you can´t...
