Can you over-water a cactus?
Cactus
Fungi, bacteria and viruses attack cacti, the first two particularly when plants are over-watered. Fusarium rot can gain entry through a wound and cause rotting accompanied by red-violet mold. "Helminosporium rot" is caused by Bipolaris cactivora (syn. Helminosporium cactivorum[107]); Phytophthora species also cause similar rotting in cacti. Fungicides may be of limited value in combating these diseases.[108] Several viruses have been found in cacti, including cactus virus X. These appear to cause only limited visible symptoms, such as chlorotic (pale green) spots and mosaic effects (streaks and patches of paler color).[109] However, in an Agave species, cactus virus X has been shown to reduce growth, particularly when the roots are dry.[110] There are no treatments for virus diseases.[108]
Parodia leninghausii
As most of the cactus, they need well drained soil, sunny exposure, regularly watering in summer and not at all in winter. In temperate climate, keep them outside in summer. In the wild and in winter, plant accepts frost at -4 °C if totally dry. In cultivation, it is preferable to keep cold temperature, but more than +2 °C.