Question for the experts

Over the weekend it was discovered that our observatory housed club RCX400 14" has mold growing on the primary. One spot is about the size of a nickel with a few other smaller spots. My question is whether this causes permanent damage to the mirror coating and will require recoating or if it can be carefully cleans off with no long term effects.

Thanks in advance,
DanL

Danl,
Not only will it damage the coating, it will etch the glass! You need to clean it quickly before the acids it excretes do too much damage. Chances are, the coatings may already be damaged, but the size of the spots left behind will not effect the image by much.
A desiccant plug should be placed in the focuser when the scope is not in use.

I'd get that stuff off of there ASAP. Maybe leave a
heater or heater strap on the scope on low to help
keep it dry; dessicant plugs help, too. I've
cleaned some that turned out like new, but I would
not take any chances.