Well it's obvious that it doesn't get enough light (look at that etiolation). It may well be getting too much water, because that soil looks like peat to me.

It's right by a south facing window and gets sun all day (in the summer). The photos were taken an hour after watering it (I water about a cup once a month - is that too much?

From what the plant is telling me, it's not getting enough light. That's why it's etiolated.

Soil should probably be better drained, and dependent on species (and what climate it originates from), there may need to be a dry dormant season in which it doesn't get any water. Normal procedure if the potting media were appropriately water NON retentive, would be water till the water runs through as needed. That might be every week during the growing season outdoors and every three months during dormancy (if applicable).

Sometimes the sunlight from a south facing window is not enough.

I’m gonna echo what everyone else is saying, your cactus needs more sun, and will continue to grow weak lanky growth if it continues to grow in the same spot in your house.

Here’s a pic from Google of an etiolated cactus.

Another etiolated pic from Houzz.

All the growth above the red light is etiolated growth.

I believe your cactus is an Echinopsis, possibly a Trichocereus hybrid.

Do you live in a climate where you can keep outside?

Unfortunately there is no reversing this type of growth. The only thing you can do is give more light and go from there.

Your cactus will sort of look like this after a couple yrs of growing in some nice sun.

The above cactus was in too low of light and grew skinny. The robust top growth is how it should look.

Next topic of concern. The area you’re concerned about looks to be corking. If the area is hard and bark like then it’s ok.

Cactus will get damaged and heal itself with corking, similar to how we scab and scar.

Here’s some corking on one of mine. I have zero clue what happened, but the cactus is fine, just not very pretty;).

Oh ya good catch Liz I forgot to mention that because I was babbling:).

It‘s could be scale or scars from cactus stabbing earth other. They kinda look alike sometimes.

An easy way to check is the scale should come off fairly easy with your fingernail. If they’re scars you won’t be able to remove without taking chunks of the cactus with the scar.

Check in between the ribs and around the areoles because that’s where pests really like to go and hide.

I was wondering about same as Liz pointed out. Brown spots seem too regular in shape to me to be anything but bugs. BUT, maybe I am wrong.

They will die on direct contact with rubbing alcohol; if they do not rub off on q-tip, they are not bugs. Rubbing should not be hard and too long. Just make sure rubbing alcohol gets directly on them. I am suggesting a q-tip because of spines of cactus. Otherwise, using a fingernail will work.

I tried to scrape it off with q tip dipped in alcohol so doesn’t seem like it’s scale or bugs?!

Check the areas I drew yellow lines, those are the areas that worry me the most.

See if you can get those pieces off. You can use an old soft toothbrush with rubbing alcohol, and if they come off it’s scale.

But like I said sometimes cactus are so close they poke each other and overtime those spots can look like scale. Especially with cacti like yours that have thicker spines. I’m gonna guess when you bought yours they were all crammed together in one pot, then once you separate the little pin pricks heal, and you get scabs that look like scale.

Ok so I was able to scrub some off with a wooden stick and o went super aggressive on some and actually injured the cactus on multiple places ( it you can see the inside of the cactus because of the scrubbing). so some parts came off and some wouldn’t. So how do I treat it for scale? And the bits that came off are on the soil now all over the place.. help me 😩😩😩

I think you misunderstood. If the circular things came off easily with the application of rubbing alcohol then they are likely scale. If they didn't come off easily then they aren't scale and probably just some sort of scarring or corking. No need to worry about the circular marks if they aren't scale. To me the round things didn't look like scale but I rarely have scale on my cacti so haven't seen them in person very much. Perhaps they aren't much of an issue in my area.

If the cactus were mine I wouldn't have worried much about the white patch which looks like scar tissue to me. Looks like maybe something happened there, perhaps a bit of rot or a bruise, but the cactus managed that injury and successfully dealt with it. There is a bit of lighter green tissue around the white patch- a margin. I'd keep an eye on the margin of lighter green tissue to see if it is changing color or spreading. If not then I'd conclude that whatever caused the white patch was contained and no longer a concern. If the margins do change then I'd think there is an infection spreading.

Thank you everyone so much for all the responses! The spots didn’t come off (without a fight) so I’m going to assume they’re not scale but will keep an eye on it as well as the white patch 😊

Water it more often. A cup a month will eventually kill it from underwatering. Water it well and let it dry out fully before watering it again. Many people kill their plants from thinking they need little water.

ohhhh ok. I’ve always been terrified if over watering it, how often would you say to water it in the summertime?

Water when needed: check the soil deep into pot. You ca do it by sticking your finger in, but I find it better if using wooden/bamboo chopstick, skewer or thinner stick (sharpen the end somehow). Even pencil will work. Stick it deep into pot - 3/4 deep or more, and leave in for few min. If dry and clean when pulled out, soil is dry and should be watered well. If moist, soil is still damp and wait bit longer.

If you keep succulents cooler in winter, it needs to be watered less or even not at all. Low temperatures ad wet soil are not good for succulents. Nobody can tell you exactly how often, since it depends on your growing conditions. It would also grow better if you could keep it outdoors in Spring to Fall. Garden, patio or balcony are great if you have access to either.

ETA: I suggested using moistened q-tip and not using excessive force ('fight') to check the spots...Kara gave you another great tip: using old soft toothbrush.

Thank you! I will be changing the soil mix to better draining and check water I needs. As for the scale.. I tried with a toothbrush and moistened q tip again and they don’t come off without force. I can take another pic of the damage I did when using force previously to what it looks like now and other parts of the cacti too.. this is weird and kind of concerning since I have no knowledge what so ever 🤷🏼‍♀️🤦🏼‍♀️

It’s not scale don’t worry;). Scale are like little suction cups, they’re not imbedded into the cactus. They come off fairly easy. The areas you went a little rough with keep dry and let scab over. It will be fine:).

Phew ok! It has a lot of brown spots mainly on the bottom of it so it must just be corking of fungal disease.. I’ll add a better pic today!

Don’t worry about the corking it is what cactus will do over time.

It’s not perfect or pretty...

But it helps support the weight of the cactus, and adds strength for new top growth:).

Corking could also be scars from old wounds. The below Opuntia started to rot , but the cactus healed itself.

Mine doesn't look quite like that.. I'll attach a pic tonight so you can see. Thank you so so much :)

I know that you mean well, but stop torturing the plant using force to determine if the spots are corking or bugs...bugs should come off quite easy as long as you apply rubbing alcohol directly on them. Since they didn't (or did wen you used too much force), looks like they are not bugs...Plant is going to have lots of scabby spots where you scratched it...

I know.. I regret using force.. bad cactus mama 😬😂 guess I was terrified of the bugs spreading and that didn’t turn out to be the case. thanks for your comment I promise I’ll stop!

Those dark spots are hairy and come off easily (I discovered this when I went too rough on the brown spots), those dark hairy spots are on other parts of the cactus too. I will post pics of the rest of the cactus tonight so you can see the extent of the spots

Those spots circled in orange look like spent flowers to me. Cactus flower tubes often have some sort of spines or hairs on them.

Oh gosh, I went nuts when scraping off the brown and hairy spots that I removed most of the flower tubes 🤦🏼‍♀️🤦🏼‍♀️🤦🏼‍♀️😐

Don’t worry I’m pretty sure those are aborted buds from awhile ago.

I‘ve got some leftover on my Trichocereus from last yr.

Did you ever get to see the flowers on your cactus?

No I didn’t! And I’ve had it for about 3 years now..

Once you start giving more light and it gets nice and happy you’ll get to see them one day.

Also here’s a pic of my (believe old man cactus) that has suddenly turned brown ish up top?! 🥺

Your first cactus looks healthy besides the etiolated bits. My only advice for him is to acclimate to stronger light.

Your second cactus which is a Cleistocactus strausii aka Silver Torch cactus it’s hard to say whats really going on because the spines are in the way;). Do the brown tips feel soft? Should be firm like the rest of the cactus.

I tried to stroke it a bit and it doesn’t feel much different than the rest of it. I know that’s why I just noticed it, it’s a hairy one 😂

I wouldn’t do anything yet, but just keep your eye on it.

If you notice quick major changes like the tip getting darker, mushy, or dry and thin then post again and someone will help:).

Thank you, much appreciated! 😊