Good morning and thanks for your timely question. Timely because I have found gray mold, botryitis, on my verbena. i believe mine was caused by the dark rainy weather that we have been experiencing the last week or so.
Yours may be from the same or it may have come from the place that you bought it. The mold or fungus can be present in the soil that the plants are potted up in.
I have sent you a very informative article from Penn State U. extension on the subject.
The plant needs to be cleaned up, thinned a bit for better air circulation and let it dry out a bit. Make sure it gets plenty of sun.
Another website for informative searches is from The Ohio Stats Univ. It is called Ohioline. Feel free to use it anytime. I do!
I hope this answer helps. You were on the right track and your geraniums can be saved.
Thank you!







http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/botrytis-or-gray-mold






http://ohioline.osu.edu/