@Psilocubensis, sulphuric acid is used simply to lower the pH of the nutrient solution, the tap water here is 8.4pH so after mixing usually it's above 7pH before regulation with sulphuric acid.
The citric acid is used to lower the pH further so a pH range is covered over a few hours as the pH naturally rises from the break down and plant uptake of the citric acid. But citric acid has another benefit, if you look up the Krebs Cycle you will find it's actually called the citric acid cycle too, and it's all to do with cell energy production and electron carrying etc throughout the plant. I wouldn't grow a plant without it
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