Hi fellow gardeners, I need some help with my little cactus pup please.

I planted it last August (winter in sydney). It was pulled off a mother plant, placed in a bowl for a couple of days to dry before planted into soil. It was healthy, full and bright green at the time. Note it's very tiny about a few cm tall only.

Since planted, we watered it every once or twice a week, the soil drains well via a hole. It was placed in a bright area with indirect sunlight. However it was always a bit sloppy to the touch.

In October, I pulled it out to check and see it had grown a few roots. The size of the plant didn't change but the spikes slowly started turning red (that's how the mother plant looks). But the body was still a bit sloppy.

During the last few months (summer) I started to notice it shrinking in size, color darkening and even sloppier. Upon inspecting the roots I notice they haven't changed in number or size. I thought that due to the heat it needs some more watering, hence started to water every few days / one week. Most of the time we only drizzle a bit of water and only wet the top layer of the soil, occasionally we give it a full water through until it drains out of the hole. Before we water we check to make sure the soil is dry.

Nothing has improved in the last few weeks, today I pulled it out again to inspect the roots. I notice one root has dried up, the other one looks okayish. Neither are wet or squishy, so they don't seem rotted to me. The plant has definitely lost size and is quite soft though.

Any ideas what has happened to it and how could I save it? It has special meaning to it (was a gift when me and bf went official) so we reeeeeally want to save it!! Any help would be appreciated, thank you so much!

First congratulations the photo when you first got it is so heartwarming

I was hoping someone who grows cacti in the C&S forum can help answer your question.

I think the pup is just too small at this time that it is having a hard time adjusting to its new home. It is probably shrinking as it uses its own water while reestablishing its roots so it can accept water. You seem to be doing it right, misting or watering only when soil is dry.

However you should refrain from trying to take it out to check for roots. Every time you do that it has to reestablish again. I hope 🤞 it bounces back for you. If not, it has served its purpose and you have a photo to remember it and you have each other, which is more important.

Every time you dig it up it disrupts those tender new roots and breaks off the fine rootlets that are just developing. It is trying to start up, but your inspections are setting it back.
I suggest you put it by the window and ignore it for awhile. If you see new growth, you'll know the roots are growing too.
Continue to be very careful about watering, as it is in the wrong sort of soil. I'm not sure it would be good to re-pot it now, it's at a very delicate stage, trying to grow roots, which need to be undisturbed.
Desert cacti are very difficult to grow indoors, it's hard to get the heat, light and water just right.

So far, based on your photos, I think it is still alive. But being too small, it is just slow going. Ideally, baby cacti needs to stay a bit longer with its mother plant at least reach about half the size of mother plant, before being separated from it.

It still has some viable potential. Just be very patient. Looking at that container, it is still too big for the size of your plant. If it were mine, I would further reduce the size, still with a drain hole, keep using well draining cacti mix and be patient in waiting. Leave it be, avoid peeking below. Water as needed, position in brightest, warmest area in your house. That is all I can suggest for now. It will be a long wait for sure. So patience will be your friend. Good luck!