I'm not buying your idea that acids used to ph water build up in the soil! There is no evidence to support that. the acids used for ph adjustment breakdown, just like everything else. Acidic soil is caused by the plants themselves in the everyday process of of ion exchange thru the roots causing concentraions of acids. What does the roots exchange for mineral ions? Hydrogen ions (H+ ) or Hydroxyl ions ( OH- ). Plants tend to favor H+. This exchange means the plant is actively acidifying the soil at the same time as decomposition of organic matter in the soil ( and organic nutrients etc ), leading to carbonic acid buildup. H+ is acid ( PH= measurement of H+ ). the plant exchanges H+ for amonium and the soil acidifies over time. During flower, plants exchange even more H+ for more K and Mg also acidifying the soil. P uptake does the opposite, but the transport of H+ for the other needs exceeds its nulifying benefit. So it would seem to me, the issue is caused by a very active plant, or the organic matter feeding the soil.