So i recently purchased a bridgesii penis plant, to add to my cactus garden i started last year. The cactus seems healthy and appears to be doing well in its grow terrarium under t5's, but i noticed a black spot on it. I think its getting bigger, but can't be %100 sure. I do know it was there when i got the cacti.

Anyway, fast foreward a week and a half later, and i noticed a few bumps, almost like blisters on one of my bridgesii's i have in the terrarium. Two days later and they are starting to darken and turn black. More are beginning to show up and i think its starting to happen to some of the others in the tank too (8 total, 2 bridgesii montroses, and 6 regular bridgesii's).

Is this rot or anything to be worried about? I've noticed they are a more yellow towards the top recently, but i assumed that was due to me moving them from natural light in a windowsill, to a 50 gal aquarium w/ 2x 54w HO blue t5's. I also changed their light cycle from natural time to 5pm to 8am on, and off in the day when i moved them to the aquarium.

I've attached some pics, the first of the montrose that first showed signs of this, and a bridgesii that has recently started to show spots too.

If anyone knows what this is, or can tell me what to do to save them if they are infected/rotting please let me know asap. It would be very much appreciated.

I wouldn't worry about those.

My bridgesii gets them quite frequently and they don't spread or anything. I don't know exactly what it is though but I can tell you they get a lot worse if you pick at them, so just accept it as a part of the cactus.

Good advice.

They are usually cosmetic flaws and rarely become an issue.

Bridgesii acne

some of mine do the same. not sure what it is but it seems like a very common occurance amoung those who grow bridgesii.

its nothing to worry over, i think of them as beauty marks that just add to their character.

happy growing.

Yeah after a little digging it seems they are caused by over-watering and stress. Being that i have been giving them a little too much water lately, combined with a major light cycle change and a few days where temps were 15f off normal (heater left off), i think its not much to worry about.

over watering may be the culprit.

i actually have my cacti outside in full sun and the elements.

i never water them, the only time they get water is when mother nature waters them. sometimes she can overwater. i planted them in the best draining soil i could to combat it but i still have a little issues with the black spots.

really doesnt bother me because the rest of the cacti looks good and they are growing fine.

perhaps i need some kind of thin covering to allow light through but to keep a lot of the water off.

I was thinking of doing that same exact thing this morning! After a couple of days of rain, my peruvianus is getting black spots. I have several other kinds, and they are all fine including a bridgesii, but that peruvianus really doesn't like too much water. I have some quarter inch spots, but they usually dry out in a few days and scab over in a few weeks. I've never had to do surgery, but I'll need to be careful with the water for a month or so.

The spots on the cactus in the OP are nothing to worry about. Those cactus look pretty healthy. They might just be bruising from being bumped or poked with something.

damon if you think of something to use as a water shield please do share. im still pondering what to use but as the rainy season is getting near here in florida i need to get a solution pronto. i don't want to have to move them under the patio, theyll lose a lot of light that way.