Not a vitamin deficiency - plants make their own vitamins. Perhaps nutritional, but not enough info provided. Have you used anything topical on the foliage - insecticide, fungicide, leaf cleaner, homemade concoction with dishsoap or other household cleaner? How large is the pot and how do you determine when it's time to water? Does the pot have a drain hole and is the main pot slipped into another (cache) pot? Have you been fertilizing regularly? If 'yes', with what? How long have you had the plant? Does your home have an ionic exchange (uses salt) water softener?

As noted, there really isn't enough information to offer a meaningful diagnosis.

Please show an image of the entire plant, including the pot(s) it's in.

Al

The plant is 6 feet tall and I had it for 15 months. It is growing very well. Makes new leaf’s often and growing in size over all. It is in a pot with hole and sits on a metal stand few inches above the floor with tray on the floor to catch excess water. I use water meter or my finger to test dryness for top soil. Usually water once a week to 10 days.
Never used topical chemicals or substances.
I fertilize once a month or less often with fortified 20-20-20, usually several times diluted than the recommended on the bottle.

Full plant

why does the window look frosted"???

and kind of a/c ducts blowing on that window and the tree???? .. causing the window to fog like that ...

ken

The image isn't of much help because the leaves can't be seen well enough to read what might be going on.

It is in a pot with hole and sits on a metal stand few inches above the floor with tray on the floor to catch excess water. So there is a gap of several inches between the bottom of the pot and the bottom of the saucer so there is no pathway by which the water that drains from the pot can make its way back into the grow medium?

I use water meter or my finger to test dryness for top soil. Usually water once a week to 10 days. Water meters are very unreliable, and using the finger stuck in the soil to determine when it's time to water is usually a recipe for over-watering when the pot is deeper than about 5". If your pot was 10" deep, when the top 2 inches feels dry, the bottom 6" of grow medium can be 100% saturated with water. Using a "tell" you can make from a wooden dowel is much more reliable when it comes to determining appropriate watering intervals.
I fertilize once a month or less often with fortified 20-20-20, usually several times diluted than the recommended on the bottle. You're not providing enough supplemental nutrition and the 1:1:1 ratio of 20-20-20 fertilizer supplies more phosphorous and potassium than the plant can use relative to the amount of N it supplies. Your fertilizer also lacks calcium and magnesium, and derives all of its nitrogen from urea.

If you're watering correctly, so the entire soil column is being wet and at least 20% of the total volume of water applied exits the drain hole, you should be fertilizing about every 4th time you water during periods of robust growth (late spring/ summer), and maybe every 5th time you water during the darker months (Oct thru Apr), if you live in the northern hemisphere and north of about the 25th parallel. My suggestion would be to start using Foliage-Pro 9-3-6 fertilizer,

which provides complete nutrition from a single source. Fertilize at recommended rates. Also, skip the finger and water meter and use a "tell". Your plant wants more light than it's getting (low light can cause leaf shedding).

You might find this Overview of Good Growing Practices to be helpful. If put in place, it will definitely help you avoid all the major obstacles almost every grower encounters on their journey toward a green thumb.

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 plenty of air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support the kind of root health most growers would like to see; and, a healthy root system is a prerequisite to a healthy plant.

Watering in small sips leads to avoid over-watering leads to a residual build-up of dissolved solids (salts) in the soil from tapwater and fertilizer solutions, 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

Thank you