A nursery plant, a bag of fresh potting mix and an added fertiliser can all contribute nutrients to the same container. Before feeding marigolds again, check what is already part of the planting.
Read the growing-medium label and record any feed used at potting. A scheduled liquid feed should not be added automatically on top of an unknown base treatment.
Look at growth and conditions
Check light, watering and the plant's stage. Plenty of leaves with few flowers is not a direct instruction to increase the total dose. A struggling root system will not be repaired by changing the label from 'general' to 'flowering'.
Follow suitable product directions and measure any dilution. If you compare routines in different pots, label them rather than relying on memory.
Keep a note of when the compost's initial feeding period ends according to its instructions. That gives you a practical point for reviewing the routine. Container size and growth conditions also matter, so do not assume a field-grown plant and a small balcony pot should receive identical treatment throughout the season.
The RHS fertiliser guide distinguishes a base dressing mixed into compost from later liquid feeding. List both when reviewing the dose: a new bottle does not erase nutrients already added to the pot.
Related reading: Marigold Feeding: Planting, Growth and Flowering Stages.