Fungus or mold, stir with a fork or similar, reduce the amount of water by half, same frequency.

You will never be able to water properly without drainage holes in the bottom of the container.

The little white balls are fungal hyphae, common to potting medium of most kinds. The fungi is feeding on the organic ingredients that potting soils are made of......peat, bark, coir, etc. I'd not be surprised if little mushrooms don't appear at some point, the fruiting bodies of the underground hyphae and mycellium.

Your presumption that the stones in the bottom of the pot are an acceptable replacement for drainage holes and a course textured medium is not a good one. Right now, your container has no drainage.

I thought terrariums were designed exactly this way...but in any case it does sound like too much water.

This might be a good topic for the Container forum - or do we have a Terrarium forum?

Yes I thought so too, I've seen many tropical plant terrariums in non-draining containers. I will try reducing the amount of water I give. Will the fungus go away after I give it a drying cycle and/or reduce the overall moisture?

Probably not, it's a natural phenomenon of decomposition. If the potting mix was very coarse textured and able to drain rapidly and fully, you would probably never see a fungal colony set up housekeeping in the first place.

Those are soil mites.

I had this grow in a glass container that did not have drainage. I could see these white dots grow in clusters throughout the soil, both the bottom, sides and top. There was so much of it and it kept spreading. I thought it was because I had used soil from an older potted plant.

I grew next plant in a pot with good drainage and a plate to catch excess water, new soil and careful not to contaminate. I would not water excessively, but definitely stopped for a few days if i saw water catch in the plate. Same clusters of white dots growing and no idea how to get rid of it or stop it growing back (tried rinsing roots and replanting).

I have had these little creamy grains, ususally in sick plants. I'm sure they're not fungal in origin. I have found (tiny, white grubs) - root mealy bugs IN the soil of pots with this GRANULAR deposit on top - I dont know if there is a connection. I've found Mealy bugs also in pots with a white fungus - looking web in the soil.