We need a photo to better help.

"Near a window" could in fact imply exposure to cold at this time of the year.

i water it about one a week or if the soil is dry. never too much water and mist it occasionally. it is only near a window during the day but not everyday. never any direct sunlight. and i meant the vertical stem. the last couple of days the base of the stem started turning brown but it's not squishy. there is a few spots or specks on it. it's been doing great until the last month or so. it's weird because there hasn't been any changes in its behavior or ours before then. maybe just have to wait it out. thanks for taking the time to read

The leaves look stippled, like when a plant has a mite infestation.

Re watering intervals: whether or not you should, shouldn't, or can with impunity water on a schedule depends on the physical properties of the planting medium you use. Because of the media I use, I can/do water EVERYTHING I grow on a very regular schedule, and I have no trouble keeping plants in a high state of vitality. That said, and based on the appearance of the medium you're using, you would be much better served to water on an as-needed needed basis rather than on a schedule, this, because the soil is too water-retentive to water any other way.

The green stems of schefflera turn brown as the outermost layer of living periderm dies to form the first layer of corky material we call bark, so the 'browning' stem might be a natural part of the plant's morphology. Too, the spots or specks on stems and branches could be lenticels another normal part of of morphology. There's no way to tell w/o better images, but I can see lenticels and areas where green periderm is turning corky.

So, I suggest you start using a 'tell' to 'tell' you when it's time to water (more about a 'tell' below). You can also learn to tell (for now, while the plant is still small) if the planting needs water by hefting it. It will become MUCH lighter when dry then it is immediately after watering. You decide between hefting and using a tell after you read what's below about the 'tell'.

If you do this when you water, you can eliminate about 100% of the potential to over-water: When you water, make sure the entire volume of the medium moistened. After the pot has stopped draining, hold it over the sink or a tub and move it up and down. You'll immediately see that on the reversal from downward movement to upward movement, a measure of water will exit the drain hole. The sharper the reversal from down to up, the more water exits, though the amount diminishes as excess water continues to be forced from the soil thanks to the harnessing Newton's first law of motion. This works exceptionally well for all plantings light enough to be manageable, and there are other 'tricks' that utilize simple science that can help with larger plantings.

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

Also that mix looks very slow draining, I see only the center of the soil is wet. if mine, I'd add at least 50% Perlite to it to improve its drainage.

Given the appearance of the soil mentioned by Karen, ie only wet in the centre, could it be that the water, although applied on a schedule was only applied in small quantities rather than a less frequent thorough drench and drain?