Use a 'tell' to check moisture levels. I'll leave something about using a 'tell' below. The necrotic leaf tips are from over-watering or a high level of solubles (salt) in the soil. You should be flushing the soil when you water. If you can't, for worry that the soil will remain wet for an extended period, you should consider a more appropriate medium and/or learn how to mitigate the effects of excess water retention via the use of ballast, wicks, or other effective measures that help control the amount of water your soil can hold.

AFTER you flush the soil thoroughly, you can start fertilizing regularly. If you start fertilizing now (before flushing), and all or part of the necrotic leaf tips are attributable to a high level of salt in the soil solution, you'll only add to the problem. 3:1:2 ratio fertilizers are probably the best bet. The best I've found in that ratio is Foliage-Pro 9-3-6. I use it for everything I grow, though I do 'doctor' it for a couple of plants like hibiscus and tomatoes.

Appropriate Medium

From my perspective, an appropriate medium is a
medium that allows us to water to beyond the point of saturation at
will, so we're flushing the dissolved solids (salts) that are present
in tapwater and fertilizer solutions. These dissolved solids are left
behind and accumulate in soils whenever we're forced to water in
sips, which is commonly employed as a strategy in order to avoid the
sogginess that limits root function and wrecks root health. It's
important to realize that a healthy plant is not possible w/o a
healthy root system. If you have established goals that include
healthy and attractive plants, it's critical that you have a plan to
avoid the limitations imposed by over-watering and an accumulation of
dissolved solids (salts) in the soil solution.

Not every grower fully understands the dilemmic
issues associated with inappropriate soils that force the plant to
pay a vitality tax resultant of an unhealthy amount of water being
retained for extended periods when we water correctly – which is to
say, when we flush the soil to limit salt build-up. On one hand, we
have the potential for over-watering, and when we act to avoid it by
offering dribs and drabs of water here and there, we have high salt
levels to deal with. It's easy to see how we all might benefit from
use of a soil that allows us to water so we're flushing away excess
salts without limiting our plant's vitality via waterlogged soils.

Flushing Soils

Water-retentive soils that can't be flushed during
our regular water applications need to be flushed regularly to ensure
salts from tap-water and fertilizer solutions aren't accumulating in
the soil and limiting the plant's ability to take up water. To flush
the soil of a planting: Water with room temperature water until the
soil is completely saturated. Allow the planting to rest for 15
minutes to an hour to allow as much of the salt accumulation as
possible to go into solution, then pour a volume of room temp water
equal to at least 10X the volume of the pot the plant is in slowly
through the soil. This will remove most of any accumulation of
offending salts and resolve any skewing of nutrient ratios.

It's a good idea, no matter what time of year, to
fertilize most plants immediately after flushing the soil. Try to be
sure you're using a fertilizer that has a ratio as close as possible
to the ratio at which the plant uses nutrients. The NPK % listed on
fertilizer packaging is not its ratio. 7-7-7 and 14-14-14 are 1:1:1
ratios. 9-3-6, 12-4-8, and 24-8-16, are all 3:1:3 ratios. Container
growers should try very hard to avoid use of fertilizers advertised
as 'bloom-boosters', or any number with a middle number (Phosphorous)
higher than either the first or third numbers (Nitrogen or
Potassium). These fertilizers can badly skew nutrient ratios with
even the first application). On average, plants use about 6x as much
N as P, so there is NO potential for a positive outcome when
supplying many times as much P as the plant requires. I, and a large
number of other members, use Dyna-Gro's Foliage Pro 9-3-6. It's
designed to closely mimic the uptake ratio of the average plant, and
has many other attributes not commonly found in other fertilizers. It
also has ALL of the nutrients essential to normal growth. Summarized,
it makes fertilizing as easy as it can be, and from 1 container.

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