Where do you get your water from?

How wet is the bin? Is it dripping wet? Is there a cover on it?

Since I had some available, I've been using distilled to keep it damp, but not dripping wet, when it gets dry. Yes, it's covered.

I started this bin in the spring and it's been trouble-free. The worms seem pretty happy and the population has noticeably increased. The layer of fresh, torn newspaper was put in just a few weeks ago and was my first addition of new bedding.

Distilled is a good choice, it should be bacteria free. It could be lack of air flow? Try leaving the cover off.

Maybe I'll increase the air to see if that helps.

I'm not sure that I agree with any concerns over adding bacteria, or that my tap water might somehow be a source. I was looking to avoid chlorine.

Avoiding chlorine is also a good choice.

I would leave it alone unless you can tell that it's causing problems. The mold is decomposing the newspaper. That's good. If you need to stir it up for other reasons, fine, but no need to try to kill the mold itself.

I wouldn't worry about it unless it smells bad or the worms are trying to escape.

Im thinking its a lack of air flow. If I put starbucks coffee grounds in a 5 gal bucked with a lid on it will develop mold. I dont worry about adding this to my bins but have never gotten mold in my bins or mold to develop in a bin. I also dont make a point of adding chlorine free or distilled to my bins , doesnt seem to be a concern , wormwise.

I dechlorinate tap water by leaving it in an uncovered bucket for a few days. The chlorine/chloramine will evaporate out of the water. Like hummersteve I don't go to the bother or expense of buying distiller water. When I get rainwater I use it. Otherwise I just let it evaporate away from tap water.

Though we also dechlorinate our tap water we use for watering the house plants by leaving it sit in watering cans until we need it, there is another way to very quickly and cheaply dechlorinate tap water (we do this for the koi pond). Use Sodium Thiosulfate... just add a single tiny crystal per gallon of tap water and stir... instantly dechlorinates water. You can get a pound of it very cheaply online from any chemistry supply store... and it will last you a life time because the quantity you need is soooo tiny.actually a tiny single crystal will probably dechlorinate 10-15 gallons of tap water (depending upon a few factors specific to your local water supply). And its use is very safe... I've accidentally spilled a quarter cup of crystals on plants and into the koi pond with absolutely no ill effects on fish, plants, or microbial balance of the pond system. I've used it around the fish and garden ponds for more than a decade without issues of any sort.

From Wikipedia: "Thiosulfate occurs naturally and is produced by certain biochemical
processes. It rapidly dechlorinates water and is notable for its use to
halt bleaching in the paper-making industry."