"Salinity and acidity
Salinity, toxicity and extremes in soil pH (acid or alkaline) result in poor biomass production and, thus in reduced additions of organic matter to the soil. For example, pH affects humus formation in two ways: decomposition, and biomass production. In strongly acid or highly alkaline soils, the growing conditions for micro-organisms are poor, resulting in low levels of biological oxidation of organic matter (Primavesi, 1984). Soil acidity also influences the availability of plant nutrients and thus regulates indirectly biomass production and the available food for soil biota. Fungi are less sensitive than bacteria to acid soil conditions."
I say test the runoff first rather than screw with the beneficial bacteria in your soil or grow medium if yo don't need to. If your water is a pH of 8.0 then heck yes drop in some lemon juice or acid. But a pH of 7.0-7.5 is usually fine for soil. Just my opinion.