Supposedly Excel only has about a 12 hour effectiveness in the tank water. So time and water changes should set things straight.
How quick was the plant damage after the accident? How are the inhabitants?
Accident happened on Monday around maybe 6p. I noticed the damage when I got home at 8p Tuesday, so I'm not sure other than "within a day". As far as I can tell none of my fish or snails are acting any differently.