Impatiens like moist soil, not saturated soil. Soil that is too wet will cause the lower leaves of the plant to go yellow and then drop. In serious cases, you can defoliate the whole plant. Dark leaf spots can be caused by bacteria, fungi, or occasionally viruses. The most common dark spots will be caused by humid conditions and wet leaves. Plants which are overwatered are particularly prone. Strong healthy growing plants are not usually infected. Treat your plants correctly and the infection won't spread. You might want to remove obviously infected leaves just to help.

thank you shrubs n bulbs. THAT is exactly what I'm doing at the moment and keeping my fingers crossed. I am letting them dry out a bit.