How good of you to take in this plant and care for it! Have you checked for root rot already?

You would need to remove the plant from the soil and inspect the roots. If there are still good, healthy roots, you can trim back any rot, and if possible apply a fungicide to the remaining healthy roots and then re-pot it. Make sure to use new, clean soil as needed.

Sounds like you are doing all the right things otherwise as far as only watering when 1" is dry and good, indirect sunlight.

I’ll give that a try! Maybe you’re right, there’s some root rot going on in some places that’s hindering the plant from making a full recovery. Also, I don’t know how old this soil is so probably clean, fresh soil would help! Thanks!

First, the plant is seriously starved for light and appears to be over-potted, which would increase the potential for limitations on root health/function. It also looks like there are nutritional issues going on. Please describe you're doing insofar as nutritional supplementation.

Whether the soil is new or clean is a secondary consideration to it's structural state. Replacing one water-retentive medium with another water-retentive medium isn't going to improve root health/function unless you get your watering under control. The best way to determine whether or not a large plant needs water is by using a 'tell', which is no more than a 48" dowel rod (5/16" works very well) cut in half and ends sharpened in a pencil sharpener.) I'll leave you something about that after my offering.

Imagine you're on a teeter-totter that is 2 miles long and a mile high. As long as we're putting an image in your mind's eye, we might as well put a handrail on both sides so you don't fall from ahigh. Trying to grow in a poor medium is like trying to walk up one side of the seesaw toward the fulcrum. It's hard. If you don't get to the top so you can cross the fulcrum and get to the downhill side, you'll be forever in a battle with your medium for control over your plant's vitality, and you can count on your plants losing a large % of their potential. A good medium is THAT important. Being able to water to beyond the point of saturation (so you're flushing the soil of accumulating dissolved solids [salts] when you water) without the plant having to pay an over-watering tax on vitality (health) due to extended periods of soil saturation, is a key element in helping your plants realize as much of their genetic potential as possible. If you adopt that attribute as a minimum standard for your choice of medium growing suddenly becomes much, much easier. An appropriate medium also makes fertilizing monkey easy, whereas fertilizing soils that are too water retentive usually amounts to a best guess and a wish or prayer.

If you're not someone who wants to get overly involved in making your own soils, you can solve the over-watering issue by using ballast to solve excess water retention. While ballast can almost entirely remove excess water retention, it doesn't ensure the high levels of aeration plants thrive on, and it can't prevent the structural collapse of media with very large fractions of fine materials - peat, coir, compost, composted forest products (the equivalent of mystery meat) sand, topsoil, ......, others.

You might also find this overview interesting.

Using a 'tell'

Over-watering saps vitality and is one of the most
common plant assassins, so learning to avoid it is worth the small
effort. Plants make and store their own energy source –
photosynthate - (sugar/glucose). Functioning roots need energy to
drive their metabolic processes, and in order to get it, they use
oxygen to burn (oxidize) their food. From this, we can see that
terrestrial plants need air (oxygen) in the soil to drive root
function. Many off-the-shelf soils hold too much water and not enough
air to support good root health, which is a prerequisite to a healthy
plant. Watering in small sips leads to a build-up of dissolved solids
(salts) in the soil, which limits a plant's ability to absorb water –
so watering in sips simply moves us to the other horn of a dilemma.
It creates another problem that requires resolution. Better, would be
to simply adopt a soil that drains well enough to allow watering to
beyond the saturation point, so we're flushing the soil of
accumulating dissolved solids whenever we water; this, w/o the plant
being forced to pay a tax in the form of reduced vitality, due to
prolong periods of soil saturation. Sometimes, though, that's not a
course we can immediately steer, which makes controlling how often we
water a very important factor.

In many cases, we can judge whether or not a
planting needs watering by hefting the pot. This is especially true
if the pot is made from light material, like plastic, but doesn't
work (as) well when the pot is made from heavier material, like clay,
or when the size/weight of the pot precludes grabbing it with one
hand to judge its weight and gauge the need for water.

Fingers stuck an inch or two into the soil work ok
for shallow pots, but not for deep pots. Deep pots might have 3 or
more inches of soil that feels totally dry, while the lower several
inches of the soil is 100% saturated. Obviously, the lack of oxygen
in the root zone situation can wreak havoc with root health and
cause the loss of a very notable measure of your plant's potential.
Inexpensive watering meters don't even measure moisture levels, they
measure electrical conductivity. Clean the tip and insert it into a
cup of distilled water and witness the fact it reads 'DRY'.

One of the most reliable methods of checking a
planting's need for water is using a 'tell'. You can use a bamboo
skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm)
would work better. They usually come 48” (120cm) long and can
usually be cut in half and serve as a pair. Sharpen all 4 ends in a
pencil sharpener and slightly blunt the tip so it's about the
diameter of the head on a straight pin. Push the wooden tell deep
into the soil. Don't worry, it won't harm the root system. If the
plant is quite root-bound, you might need to try several places until
you find one where you can push it all the way to the pot's bottom.
Leave it a few seconds, then withdraw it and inspect the tip for
moisture. For most plantings, withhold water until the tell comes out
dry or nearly so. If you see signs of wilting, adjust the interval
between waterings so drought stress isn't a recurring issue.

Al

It needs to dry out being indoors in a big pot. If you want to see new growth leave it dry for a few weeks. It still needs a lot more light then you should see the leaves getting bigger.

Leaving F elastica dry for a few weeks results in loss of foliage - probably all foliage; and, low light conditions produce larger leaves and long internodes, which contributes to rangy, coarse growth, especially if the grower is using a fertilizer that gets its N from urea.

High light conditions produce short internodes as well as more and smaller leaves, which helps produce a full and more compact canopy, which is highly desirable. Avoiding fertilizers that get their N from urea contributes to tight growth and a full canopy.

Al