How long have you had the plants and how long have the plants been in the same pot? Do you flush the soil when you water, i.e., water until the entire soil column is wet and at least 20% (roughly) of the total volume water applied exits the drain hole? Do you allow the plant to 'reabsorb' any water that collects in the collection saucer? When did you last fertilize? with what?
The plant has the look of one that is either in extreme need of nutrients, or one that has a high level of dissolved solids (salts) in the soil. Dissolved solids accumulate as unused nutrients and/or as the minerals in your irrigation water accumulate. This affects nutrient uptake in several ways, 1) high salinity limits water uptake, 2) since it limits water uptake, and nutrients are assimilated via the nutrient stream that depends on water for delivery of the nutrients, it therefore limits the amount of nutrients taken up, 3) high salinity is almost always accompanied by a type of deficiency, antagonistic deficiency) that occurs when too much of nutrient A can affect uptake of nutrient B, C, D, ..... . Example: Use of high phosphorous fertilizers ("bloom-boosters") for containerized plants can limit uptake of at least 6 nutrients, nitrogen, potassium, calcium, copper, zinc, and especially iron, so the balance of nutrients in the soil/ soil solution is important.
Other potentialities include over/under-watering, soil compaction, root congestion, insect herbivory, and the possibility of downy mildew or, downy impatiens mildew, or other pathogens that commonly attack weakened plants.
Answers to the questions would help narrowing down the issue.
Al
