Looks like the plant is in the process of shedding the leaf. Do check for the possibility of spider mites. The lesions on the underside probably represent the natural progression of a reaction to particular cultural conditions that cause something called oedema. Al

Aside from a possible pest that is sucking the leaf juices and causing the leaf to show brown spots, it is suggested it might be from being in a drafty location. If the plant is near a door or window and the air on the other side is cool (cold), that could cause what you see. If the plant is near a heat vent and such air current hits the plant, that also might cause what you see. Houseplants don't like an abrupt change of temperature and react badly to it. The plant does indeed appreciate good sun...not direct sun...but at this time of season the north window is not good enough. Try if you can, giving it a west or south exposure. At this time time of season, the winter solstace is fast approaching.(December 21)..the shortest day of the year. So try to give your plant as much sun as you can without putting it directly into the window which might increase through the window glass any heat build up. Water only when the plant is allowed to dry down...then water to drainage and dump the excess. Don't let your plant sit in that drainage water for any extended time. Until the plant improves, STOP all fertilizing. Feed only a healthy plant. Ficus are encouraged to be re-potted only when the pot is threatened to break.

I did not ask this question before. The one in the living room may get a bit of cold air when i open my front door when im coming in or exiting and i did water it not very long after i purchased it.

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