Before you change anything
Note which leaves are affected and when the change began. Check the potting mix below the surface, the drainage holes and any water trapped in the outer pot. Think back to a recent move, repot or feeding. Yellow leaves are a symptom shared by several problems; their colour does not tell you the cause by itself.
Inspect leaf undersides and stem joints for insects, fine webbing or sticky deposits. If you find pests, separate the plant and identify them before choosing a treatment.
Wet soil, wilting or a soft stem base
Persistently wet mix and poor drainage can damage roots. Empty standing water and pause watering while the mix remains wet. If yellowing is progressing, the plant wilts despite wet soil, or the base is soft, gently inspect the roots rather than simply waiting for everything to dry out.
Firm roots can vary in colour. Soft, collapsing roots or tissue that slips apart are more concerning than brown colour alone. Remove clearly decayed roots with clean tools and repot into fresh, freely draining mix in a pot suited to the remaining root system. Extensive decay or a soft main stem warrants advice from a plant clinic or experienced grower.
Avoid: fertilising damaged roots, moving into a much bigger pot, or repeatedly unpotting the plant to check progress.
Spots with yellow halos: possible leaf disease
Water-soaked or dark spots that expand can suggest a leaf-spot disease, but a halo does not identify bacteria. Other diseases and physical damage can look similar.
Separate the plant, avoid splashing foliage and take dated photographs to track change. Clean tools between plants. Seek a diagnosis if spots keep spreading or new leaves develop lesions; do not choose a bactericide solely from a photograph or this description.
One older leaf, everything else healthy
An occasional oldest leaf yellowing can be normal turnover. Monitor the rest of the plant before changing its care. Several leaves yellowing in succession, especially newer ones, deserve another check.
Dry mix and a light pot
If the root ball is dry and the plant is limp, water thoroughly and allow excess to drain. Check that water reaches the mix rather than running straight down a gap at the edge. Do not compensate with daily small splashes. Use moisture and pot weight to decide when another watering is needed.
Gradually weaker growth in a dim position
Consider light when smaller leaves and stretched stems accompany the yellowing. Move towards brighter, filtered light gradually. An abrupt move into strong sun can add scorch to the original problem. Newly emerging leaves may also be lighter before they mature.
Could it need feeding?
Review the fertiliser history and whether the mix already contains feed. Yellowing alone is not evidence of a deficiency. When roots are healthy and the plant is actively growing, use a houseplant fertiliser at its labelled dilution and frequency. More feed is not a faster cure.
What recovery looks like
Take a photograph now and compare weekly. Look for fewer newly affected leaves, stable stems and, when the plant is growing, healthy new foliage. Fully yellow tissue will not return to normal green. If yellowing accelerates or the stem softens, reassess promptly instead of waiting for a promised recovery date.