Hi Mr Greenjeans,

Powdered Sodium Bisulphate hydrolyses in water to give Sulphuric Acid, which will lower pH of aqueous solutions.
You will have a mild buildup of Sosium ions in your system, but that should not be a problem if you replace your nutrient solution after say three weeks.

If you do decide to replace your nutrient solution after three weeks, you should not need to use a conductivity meter, however, I strongly advise you to have and use a good pH meter.

Cheers,
Jimr007.