The anomalously large dielectric aging in ferroelectric partially deuterated potassium dihydrogen phosphate is found to have multiple distinct mechanisms. Two components cause a decrease in dielectric response over a limited range of fields around the aging field. Substantial aging occurs on time scales of ∼1000 s after a field change, as expected for a hydrogen/deuterium diffusion mechanism. A slower component can give an almost complete loss of domain-wall dielectric response at the aging field after weeks of aging. There is also a particularly unusual aging in which the dielectric response increases with time after rapid cooling.