Here's a picture of the leaves and the whole plant:

You're over-watering, and the symptoms you show/describe are what one might expect to see from a plant being over-watered. The commonly repeated advice to "water when the top inch or two of the grow medium is dry" might work well for pots in the 5 inch deep range, but it's a recipe for over-watering in deeper pots. If a pot is 10 inches deep, the bottom 6" of the grow medium could be 100% saturated when the tip 1-2 inches are dry. Instead of using your finger as a way of measuring moisture levels at the surface of the medium, use a "tell" to determine what's going on insofar as moisture levels at the bottom of the pot are concerned. It doesn't matter if the top of the medium is dry. Large roots occupying the top of the soil serve only as plumbing and anchorage, and if you do spy very fine roots at the surface, you can count on their presence as proof that you're over-watering. Also, it's highly likely the tree is way over-potted, which will make it difficult to water correctly and avoid over-watering at the same time. Ask if you want to talk about alternatives. See below for more about using a "tell".

Most seaweed fertilizers are poorly formulated as a sole source of nutrition. The reasons are, the NPK %s rarely come close to providing nutrients in the same ratio as the plant uses them; and, it undoubtedly lacks several nutrients essential to normal growth. I grow well over 100 different species of trees and all are supplemented with Dyna-Gro's Foliage-Pro 9-3-6. It has everything your plant needs for normal growth and excellent vitality in a single product. You'll likely need to order from an online source, but it's worth the extra effort.

If you decide to do something that wet your tree's foliage, try to do it early in the day so the foliage is dry by evening. Fungi require a variable (in duration) but continuous period of moisture plus a food source or chemical activator for spores to germinate. If you limit the length of time your plant's foliage stays wet, you remove a link needed for fungal pathogens to get a toehold. Also, treatments of leaves that remove or reduce leaf cuticular wax can result in a stimulation of spore germination of some pathogenic fungi, which is why you should never use household detergents (including dishsoap) on your plants. I know you didn't mention using it, but it seemed like a good place to insert a cautionary note.

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