Hmm... So, I put this plant in a terrarium and it has been sitting there about a week relatively undisturbed, except when I just picked it up to look at it and it seemed pretty unstable. Weirdly, it seems to have detached itself from it's main roots. It has a couple little stub ones. The plant itsel...

Your seeds are growing so much faster than mine!! interesting how the arios look quite a bit like frailea seedlings when they first start getting tubercles

Maybe it needs to get watered more since it's growing more. The new leaves need water to grow.
Or maybe since they're new they aren't as accustomed to the sun.

Are they crispy or squishy?

Well, they are turning reddish brown like a grown frailea, but at one point when they were outside they were bright green then a couple hours later bright red. Watered them and the next morning green again. Just moved all my very young plants to their permanent winter home, though and they are looki...

Here's what I got so far. Some fingerprints on the glass. Carrying a fish tank on the bus is sweaty work.

could be it was having problems before you got it and it's just showing now. Does look like rot to me.

Looking at the 'free' section on Craigslist, people are giving away old fish tanks and supplies like candy. I'm going to pick one up with a hood light later this evening to move some seedlings in there for the winter. My plan is to put a strip of aluminum foil around the sides and the bottom. That a...

aw, babies! so cute and growing great

That probably explains why my frailea castanea seedlings keep turning bright red when I set them out even when it's really shady... They grew in the same pot as the parent plant.

What color is it when it's not turning red? Both parent species are somewhat glaucous (ie, blue-looking), this appearance is due to a waxy coating on the skin which helps protect it from the sun and retain moisture. They need good light to develop this, If it hasn't that would make it more vulnerab...

Keeping the pot really insulated might not necessarily be a good thing. If it gets hot then the soil could overheat the roots. To keep them warm you could try keeping them under a light a few hours a day when dormant, or maybe keeping them on a low heat pad. I killed one of my cactus one night tryin...

I stand corrected- I checked on my seedling today and found that two more have sprung up! They are still newer than the other one. I'm so happy!

Well, another update. It was the only seedling but it is doing well and growing surprisingly fast. It already is getting spines.

Doesn't sound like it was really sick, just showing a little stress. All you can do is change the conditions it's in to try and make it happier. You did, and it's looking better, so you seem to have the problem figured out. It may be that it was too abrupt of a change,you just need to harden it t o...

Then you're probably on the right track. Young seedlings are not as tough as old established plants, and that's a pretty small seedling - but you knew that. You'll just have to judge by how it responds to the conditions, and adjust accordingly. Nobody here know knows as much about those conditions ...