Do past good deeds disappear due to present sins?

The texts of the Quran and Sunnah indicate that good deeds and bad deeds are in a state of push and pull. Disbelief (kufr) nullifies all deeds, while sins lesser than disbelief do not nullify all deeds, though they may nullify some of them, as in His (Allah's) saying: "O you who have believed, do not invalidate your charities with reminders [of it] or [with] injury," and the Prophet's (peace be upon him) saying: "Whoever misses the Asr prayer, his deeds are nullified." A Muslim must be wary of sins, increase in good deeds, and hasten to repent. For whoever is truthful with Allah in repentance, his evil deeds will be transformed into good deeds.