Having finally purchased an all wood Martin Dreadnought I injured my shoulder and have not been able to play it for 2 months. All the while it was securely in its case with a sound hole humidifier. Three days ago after checking on the moisture content I noticed mold spots on the sponge. I disposed of the humidifier sponge and replaced it. Then a few days later I discovered mold spots on the new sponge. I only use distilled water. I am in a panic and don't know what to do. All can think to do at this time is to keep the guitar out of the case in the air (even though dry) and keep air circulating around it with plenty of light. I can see no mold spots on the guitar but know the spores were inside the case on the sponge. I can clean the case with a bleach base cleaner but then what. What can I do if mold gets into the guitar and how could this have happened? I have been using sound hole humidifiers for years and never had a problem. Maybe it is because I have not been playing it and just opened the case to add water to the sponge?
You keep mold spores dormant by keeping the RH below 60%. Mold spores are everywhere and on everything so eliminating them is temporary. Put a drop or two of chlorine bleach or a peroxide bleach (Oxy-whatever) in the water you use in the sponge and you can control the mold growing on it. Keep your RH below 50% in your case and the spores on the surfaces of your guitar and lining of your case will stay dormant.
are you really worried, Mold has been around since time began. the panic from mold all started from Johnny Carson's side kick Ed McMann and is BS look it up. don't worry unless it is black as night and long and wispy and after its tested it is toxic
Spores are everywhere. Just clean the sponge now and then and don't worry about it.
I have had some similar problems with old guitars when cleaning the inside with too much water. Or when I soak wood with water and put it under pressure overnight to flatten it out. In bad cases mold have come to life and made quite nasty blue stains in white wood as maple. It's hard to get rid of the stains even when sanding.
Now I always keep the cleaning cloth damp and not wet as I sometimes did before. And I know that mold stains can appear when soaking and pressing.
Thank you all so much for the feedback and I will keep the sponges more on the dry side and add some drops of bleach.