a ton of tiny white worms in mostly unoccupied tank??

short video

i've had these in my tank (which is currently cycling and only home to plants, driftwood, and some snails) since a few days after i set it up (two? three months ago?) but never this many!! i did a water change today and they must have been hiding in my filter or something because it did its usual spit-up when i started it again and now they're EVERYWHERE just wiggling around the water column.

i was planning on getting goldfish this/next week but this makes me a little nervous. goldfish are little piggos and eat up everything they can so i wanted to make sure these things aren't going to be bad for them. so what the fuck are they??

if they're not bad, should i not feed so much the first few days i have my fish? because there are a LOT of them in here, as well as a few very small bite-sized snails that hitched a ride on my plants and i figure the fish will probably solve both of those problems fairly quickly.