One yellow leaf at the base of an otherwise healthy plant may simply be old. Several yellow leaves appearing together call for a closer look. Before reaching for fertilizer, note which leaves changed first, whether the soil is wet or dry, and what changed during the previous two weeks.
Start with the soil
Push a wooden skewer into the root zone or lift the pot to judge its weight. Soil that remains saturated limits oxygen around roots; severely dry soil can also cause yellowing after the plant draws down stored water. The useful question is not “How often do I water?” but “How quickly does this plant use water in this position?”
Read the pattern
Older leaves yellowing evenly can accompany normal turnover or limited mobile nutrients. Yellow tissue between green veins, damaged margins, isolated spots, or pale new growth suggest different causes. Also inspect leaf undersides and stem joints for pests.
Change one variable at a time
Correct obvious drainage or light problems first, then watch the newest growth. Removing every imperfect leaf at once can hide whether the problem is still progressing. Keep a dated photo so you can compare rather than relying on memory.