Philodendron bipinnatifidum. Is it the oldest leaf that is doing that (the lowest leaf on the stem?)

The pot looks kind of small for the size of the plant. If it is drying in 4-5 days but you are watering once per week, it would be getting too dry. If it is still moist after a week, it may be colder in the room than this plant would prefer, and/or not have enough air movement. Most Philodendrons are fine with no direct sun, but this one really does better with at least some.