I am guessing you have a watering issue. You say you water it when the top of the soil is dry, but how far down do you let it become dry before you water it. It is a plant that likes to always be moist, but never wet. It is a weird plant in that when it is young it starts growing in the ground, a terrestrial plant, but as it ages it become an epiphytic plant. Epiphytes do not have typical roots. The roots they do have are very sensitive to being over-watered.
The soil should be allowed to dry out to the depth of 5 cm or 2", before this plant requires more water. or better yet use a bamboo chopstick to measure how wet the soil is. Insert the stick into the soil. Leave it in the soil for 30 minutes or more. Afterwards pull it out, look at it, feel it. You should be able to tell how moist the soil is from the stick. You should be able to tell if it's feet are wet. Every time you think of reaching for the watering can, first reach for the stick.
The problem of being over-watered probably started at the store. You have no way of knowing how well it was taken care of by the staff at HD. Plants for those stores are a lost leader. They are not marked up at all. You pay the price they pay. It is a way to get you to buy the soil, the fertiliser and all the other areas of the garden centre where they do make their money. Because they are lost leaders staff are not given very good directive on how to care for the plants. So, often the plants from big box stores go through a lot of abuse before they are bought by you or someone else.
The way the marks are outlined in yellow is a sign of possible fungal leaf infection. Fungal leaf infections often have their origins in a watering issue. Once the plant get the care it needs, the infection will probably clear-up. If does not start to clear-up, try treating the leaves with a fungicide spray. Also, remove all of the leaves that are majority yellow. They are not helping the plant, but being a drain on resources.
Good Luck.
