Ha Ha Ha The soil is full of mold, bacteria, and all sorts of little critters. So are compost piles. Some in a bottle has you worried.
It probably isn't mold anyway. And even if it is, just pour it out, scoop out the mold and pour it back in, if it worries you. Where are you storing your ferts in a dark, dank celler (mold country) ? I keep mine in the fridge, sometimes that plant fiber settles in the bottom, I say, so what, it doesn't hurt anything. When I get down to the last oz or so, I just toss it in the compost pile. The PH on the GIG stuff is pretty low, like 4.5 or 5, I don't even think mold can grow below 5.
Compost from my compost pile is full of mold and other microlife, and my plants love it. They grow big fat kick ass buds that will nail your ass to the couch, stoned to the bone. If a few chunks in the bottle worry you, organics isn't for you. Organic ferts are chunky, cloudy, dark, stinky and full of life. For pretty colors, less stink and no chunks, you need chemical ferts. I'm not recommending chem shit, I'm just saying that chem ferts come in pretty colors. LOL