A lot of stores have the plants on display near a door. In northern areas, the cold air settles on these plants every time the door opens. After the plants have been in these stores for more than a week, their quality goes downhill rapidly. Their price remains the same for several weeks until they are finally put on a clearance sale.
A few of these stores have knowledgeable staff who can care for the plants. These people may or may not get around to doing the work to care for the plants; it doesn’t seem to be a high priority in most of the discount stores I have ever been in. Few of these stores have the greenhouse, lighting, or watering facilities to properly take care of these plants.
If you know a lot about plants, you can find occasional bargains in these types of stores. Sometimes there are even unusual plants that aren’t easily found elsewhere and at a good price, too. Unfortunately, many plants will look fine for several weeks after they have been mistreated. They may have been chilled or overheated while in shipment, they may have been over- or underwater, and they rarely have proper lighting in the store. Occasionally, they may be infested with spider mites or mealybugs. Both are very difficult to get rid of once you bring them home to your other plants.
The problem is that you don’t know the history of how well they were treated before you took the plants home. It’s completely normal for a plant to lose a few yellow leaves. But, if the whole plant is continuing to turn yellow, the plant may very well be dying from mistreatment with no way to stop it. The only thing you can do is give it the care a plant like yours should have and hope for the best.
Don’t give it extra water or less water, more fertilizer or less, etc. because what seems like tender loving care may push it over the edge. You need to let the plant stabilize in your lighting, temperature, and watering conditions. If it makes it, great; if it doesn’t, you did what you could. The only other thing you need to do is to check for insects and treat for them if you find any.
If you are new to houseplants, buy your next ones at a nursery or greenhouse that has plants year-round. They will help you pick the proper ones for your growing conditions, and they may have a warranty for replacing ones that have problems. There is a playlist on houseplants on the Greener View YouTube channel, and every Friday in February I am adding a new houseplant video.
