black spots on tip of cactus (with photos)

[npevey]

I need some advice on my cactus. I've had this plant for a few years, and it's always seemed healthy. It's added about three feet in growth in the time I've had it. Recently, I noticed black spots near the tip. The spots are hard and dry. I can't tell if they're spreading (yet). Other plants in the same pot don't seem to be affected. A couple of months ago, I moved the pot from in front of the window to a spot across the room where it still gets bright light but isn't in direct sun. Could that have something to do with it? Should I cut off the affected part? Thanks so much!

[Saxicola]

That move is probably the cause. Our eyes are great at compensating for light levels so to us a spot across the room looks almost as bright as a spot by the window but it isn't. I can't remember the actual ratio of light level to distance from a window, but the dropoff is enormous. Your plant is getting maybe 1/10th or less the amount of light it was near the window. I don't think the spots are a disease, so they won't spread for that reason, but if the light level stays too low more spots will probably form and the new growth will be really etiolated.

[npevey]

Thanks for the advice!