Question
I felt I should both add some detail to what i did before my plant got sick, as well as inform you of what has been happening since I first wrote you: I do very much appreciate your time and expertise....

I have a wonderful Ming Aralia, which was, until about a week or so ago, quite healthy. I admit that I can become over-attentive to my house plants at times, and given it's past vigor, I thought no harm would come from an extra watering (to flush out salts/deposits before fertilizing). To my dismay, the leaf stems on almost the entire tree were drooping by the next morning.

   I know Mings don't like 'wet feet' so I decided to let it dry out some and see if it would clear up. I used a copper soap fungicide (Concern brand) on the lower trunk letting it seep into the soil and into the roots, as well as the leaves and stems. I made sure that a lot of it seeped into and immediately surrounding the root-ball, which, after days seemed to have no effect, at least none which I could note.

   As the plant worsened, I decided to remove it from the soil it was in and re-pot it in better-draining, sterile soil. After a few days, and with the plant looking worse, (almost all leaves deteriorating rapidly), I took an emergency step and re-potted in a high peat content, well -draining, 'seed-starter' soil. I gently removed the damp roots, and found the soil around them heavy and caked-on, really saturated but not 'muck' like swamp mud or something.

Answer
My first question is, Why did you use a Fungicide on your Ming Aralia ('(Polyscias fruticosa' to botanists)?

Regardless of the original problem, it is important to point out that sterile soil is an inferior growing medium for plants.  Specialized root Fungi that grow naturally in the Soil pour vitamins and minerals into the plants they live near.  By wiping out whatever Fungal population you had in this plant's soil, you made recovery MORE difficult, not LESS.

For future reference, have a quick look at this study by researcgers at Vassar College titled, 'The effects of mycorrhizae and soil pathogens in intraspecific competition among asexual propagules of Allium vineale':

http://www.ou.edu/cas/botany-micro/bsa-abst/section3/abstracts/11.shtml

The researchers grew Allium bulbs in soil WITH the specialized root Fungi -- called 'mycorrhizae' (and don't ask me to pronounce that please).  They also grew the same kinds of bulbs in soil that was treated with a strong Fungicide, Benomyl, to wipe out all the specialized Fungi (plus any other Fungi that happened to be around).  In the end, the Bulbs WITH Fungi were healthier:  'Plants growing in non-mycorrhizal soil had significantly lower bulb mass...'  Translation: Bulbs with NO Fungus left in the soil were smaller than the Bulbs growing in Fungus-free, fumigated soil.

That's just one example.  There are a million stories like it in the big city.  'Teaming With Microbes' author Jeff Lowenfels notes, 'At least 90 percent of all plants form mycorrhizae...Without mycorrhizal Fungi, plants do not obtain the quantities and kinds of nutrients needed to perform at their best.'  Next time, before you use a Fungicide, make sure you need one.

Now, let's get back to your poor Ming Aralia which is now growing in sterile soil without the benefit of mycorrhizal Fungi.

The 'wet feet' that many plants are sensitive to has nothing to do with Fungi.  All roots need air.  This plant is one of those that is hypersensitive to lack of it.  These grow slowly (6 to 12 inches annually under optimal conditions) and need a little less attention than you are providing -- but with time this specimen could reach 10 feet or taller.  The trick for you is to get it to live that long.  It is ESSENTIAL that you AVOID REPOTTING this plant until it REALLY needs it.  Oversized pots retain water.  Although it's logical to expect a root system to thrive with all that extra space, when you are using a pot, you contain the moisture and all the air in an enclosed area.  When the air is used up, and there is H2O sitting around the roots, there's no way to get Oxygen down where it's needed.  Hello, root rot.

So when DO you re-pot?

Wait until this plant is totally rootbound.  It will dry out and need watering every other day.  THEN it's time to move up to a pot ONE SIZE BIGGER.  That pot should be Terracotta or unglazed Clay -- pores in those pots mean it's not airtight; Oxygen will flow in, Water will flow out.

Let's talk about Soil.

I'm convinced that growers plant Aralias in Peatmoss more than any other growing medium because it is light as a feather when dry.  Don't worry about giving your plant purified soil; worry about drainage and air and temperature, all of which contribute more to root rot than any Fungus that stumbles in.  And now you've set this sick plant in Peatmoss.

So now what?

Repot?

Every time you mess with the roots to repot, you wipe out all the root hairs.  They grow back, but there's a lag.  During the lag, it will wilt and weaken.  Enough times through that, and eventually it won't recover at all.

At the end of the day, here's the deal.

Ming Aralias are famous for one thing: FICKLENESS.  Ask anyone who has ever had to deal with one.  You have to know exactly how to water it, when to repot and when not to, and then you have to be familiar with all the other details that all plants need like fertilizer and light and growing cycles.  Look at this as a learning experience.  Each time your Ming Aralia gives you a hard time, think of it as a new chapter in a book on how to grow one.  Master it and you will be on a short list of people who've been there, done that.

I would start by getting yourself some more potting Soil, preferably something you make at home with a few handfuls of Bone Meal and Cottonseed Meal, Compost, Manure, Sand, Humus and High-Clay Dirt from the yard outside.  It should be lighter than air and it should have life in it -- yes, little tiny bugs that indicate the soil is not sterile.  For you, this may be too extreme.  They will all die soon enough, and leave behind lots of microscopic life that you won't even know is there -- Fungi, protozoa, Bacteria, maybe a few nematodes if you're lucky.  These animalcules will make your Ming Aralia VERY happy.  In lieu of real, free animalcules, you can purchase a $20 container of Mycorrhizal Fungi from the Garden Center that will seem psychologically at least perhaps more palatable to you.  Clip off a few of the most badly wilted leaves.  Water well with lukewarm water and place in semishade for at least a week.  Wait.  To max out your odds of recovery, if you can find a product called 'Messenger' in the garden center, pick up a very small dose and spray the roots and leaves as you re-pot; this is a nice little healing chemical that was isolated at Cornell University School of Agriculture in the 1990s and is licensed to a houseplant fertilizer company.

Easier said than done, I know.  Give up?  Drop it off at my house.

Me, personally, I think you can do this.  In fact, I know you can.