Teapot...Does your Schefflera still have Mites?

Instead of taking it outside, your plant should have been treated.
Spraying foliage with dish soap and water kills mites. No need for harsh chemicals.
Do any parts feel sticky? Do you see webbs (fine webbing?)

I don't see mold, but it looks like a darkened stem/small trunk.

Wait, are you talking about the white stuff on the soil? Or is it Perlite?

If the white stuff is mold, repot. You can use chemicals, but instead I'd repot in a well-draining soil.

If/When you repot, unless your Scheff is totally rootbound, don't use a larger size.

After repotting, place in medium light, and a drink. Don't re-water until soil is dry.

Mist 'leaves' daily, not soil, only foliage.

Once, or every other week, mist using a couple drops of dish soap in sprayer.

If you plan on keeping the long stem, stake so it stand erect, or prune off.

Keep away from a heating unit.

In Pic 1, your Scheff looks nice and green.
Remove dead/dying leaves, and prune soft or darkened wood.
Toni

Mold looks fuzzy. Is it fuzzy? Are the stems soft or firm?

TP - yes, you should repot, even though now is not the best timing. It will give you an opportunity to look at the roots and prune any roots that are compromised back to sound tissue.

It's difficult to determine if you are over-watering or the soil is too water retentive. What determines which side of the fine line you're on is the answer to the question, "Can I water this plant thoroughly, so that at least 10-20% of the total volume of water applied exits the drain hole without having concern about the soil remaining saturated long enough to cause root rot?" If the answer is 'NO', the soil is inappropriately water-retentive. If you can answer 'YES', then the fault lies with watering habits. Obviously there is a fungal issue affecting the roots that has gone systemic and is affecting the stems. It's not likely that will self-correct w/o some intervention on your part.

The 'best' soil is one that is made of predominantly coarse particles, like pine bark, perlite, Turface, crushed granite ..... anything larger than peat/compost/sand/topsoil. How much water your soil retains is directly ind inextricably linked to the size of the particles in the soil. If you want to learn more about soils, the discussion I linked to below (on this forum) will be helpful.

You'll also find that an understanding of the information in this thread about how water behaves in container soils will be a very valuable addition to your tool box. This thread has been active on the Container Gardening Forum since 2004 or 2005.

Al

Here is a link that might be useful: More about soils: if you click me, I'll take you there ....

Thank you so much! I'll post how things go.

Anyway, no more mites. The white stuff on the soil isn't perlite - I'm pretty sure it's mold and my problem was that I repotted the scheff in a pot that was too big and I overwatered the whole thing.

re: compromised roots - do you mean rotting moldy smelly wet roots? I'll look!

Did you read the links from AL? Here's another good one.

Yes, TP. By compromised roots I meant roots that are affected by rot that could spread further. If you find soft, dark, smelly roots, trim them back to what you're sure is sound, healthy tissue & repot into a soil that is durable and drains well. Please do read the links. Let us know how things go, too.

Best luck.

Al