I know my beads came with a warning to NOT use anything other than pure distilled water, so I would also advise against propylene glycol. You may have used it once and they are still working fine, but at some point it can clog the pores of the silica beads.
I used to have the same problem with my beads even though my humi was only kept around 65%. The problem is that right there on the beads it is humid enough for them to grow mold especially without any airflow on them.
The way I fixed this was by adding half propylene glycol and distilled water to a new batch of beads. After the first time you use the mixture you only need to add distilled water after that because I believe the propylene glycol stays with the beads and does not evaporate with the water. The reason why this works is because the propylene glycol doesn't let the humidity ever go above 70% rh right on the beads. Mold usually doesn't grow unless it is above 70% rh.
You can find propylene glycol by the gallon online (where I got it) or maybe at some stores.
Been working perfectly for me for at least a year now. Hope this helps!
Just to clarify
There seems to be some confusion about beads. Beads in the context here are referring to the tiny (smaller than a bb) round white (clear when wet) beads such as sold by Heartfelt. Gel also now comes in round larger clear balls. These are referred to as GEL even though they look like round large beads. I have had the GEL get black spots (mold?) but never on my beads.
Comments
There seems to be some confusion about beads. Beads in the context here are referring to the tiny (smaller than a bb) round white (clear when wet) beads such as sold by Heartfelt. Gel also now comes in round larger clear balls. These are referred to as GEL even though they look like round large beads. I have had the GEL get black spots (mold?) but never on my beads.