If the pitahaya is too watery or opens with a bit of pressure, it has already rotted and should not be ingested. Another way to know if it is bad is by smell and taste. So if the pitahaya tastes or smells bad, do not eat it and throw it away. If the pulp of the dragon fruit changes color, it is most likely already rotten, and you should not eat it. If mold develops, the dragon fruit will get black or white spots or lint on top. If that's the case, throw it in the trash immediately.