Re: How does sulfuric acid affect hardness (CaCO3) of water?

Neither the addition of sulfuric acid nor the pH of solution has any effect on hardness. Hardness is a measure of calcium and magnesium ions in solution. The acid is added to reduce scaling by keeping the "scale" in solution. As water is evaporated (the hardness chemicals stay behind), the solution is concentrated and hardness increases. More hard water is added to replace the water that evaporates.

Eventually, even pH control will not keep scale in solution. Water must be "bled" from the system periodically (often continuously, through a sump overflow or proportioning valve).