Okay so listen to this answer and try it, if you do nothing the cactus is doomed. However, I personally had the same problem when my mother passed and I got the plant that no one wanted. Every morning I empied the remaining coffee into the plant, I did this for about 3 1/2 months, the spent coffee (not the grounds) addecd just the right amount of neutrients back into the soil that the Cactus thrived and actually grew more than 1 1/5 foot taller and added just under 3" at its base. Now, that same cactus ghraces my office near my desk and is still alive, it has been watered 2x a month now for 9 years with coffee, it is doing quite well. Something to think about.