What is living in my ACF tank? Larvae? Parasites?

[Kayli]

I have 2 male African clawed frogs in a 20gallon long aquarium. My tank is filtered and kept at 70 degrees. About 3 weeks ago, I purchased a full spectrum light for my tank. It has never had artificial lighting before and that is my only recent change. Today, I took a close look and found hundreds of what appear to be some kind of larvae emerging from my sand substrate! My frogs are ignoring them, but I am very concerned and have no idea what they could be!

These are the best pictures I could manage right now, as the little pests are very tiny, maybe a quarter of an inch, and it was difficult to adjust the focus on my camera. Any ideas?