http://www.plantsgalore.com/care/soil/00-soils-Preparation-03-pH.htm
This is a chart showing nutrient availability at different soil pH intervals. If you continue to water with pH adjusted water (~6.5) the soil pH will come down to where you want it to allow for nutrient uptake to be maximized and mitigate lockout. But your seedling is fine at a slightly more alkaline pH while you work your way down through waterings.
I would have to disagree with Drumsnbuds in that pH is vital to nutrient availability in any and all media... including soil.
Most of what causes the alkalinity of soils is carbonate based compounds in the media (CaCO3 and MgCO3) ‘lime’ which will be neutralized easily through watering with pH adjusted water.