It's very hard to answer your question without seeing a picture or a video link first. It's unlikely to come from a frozen food but nothing is impossible.
If they are white, long vs round, are crawling on the glass as well as other areas, they are probably copepods which come from dirty water caused by excess food. Be more careful with the amount of food you feed so that there are no leftovers or make sure you clean up any leftovers after about 3 minutes of feeding time.
Too blurry.
See if you can siphon some into a glass or clear jar to see if they are mobile ( moving around) or if you can see with your magnifying glass if they have a mouth and legs or a foot like a snail.
Whew, at least we got them ID'ed.
Here's a good article that should answer all your questions. Water Mites Profile: Water Mites in Shrimp and Fish Tank - Shrimp and Snail Breeder
Me too,
They are not a very common pest for me but I've seen them before. I found that article quite accidentally and after reading it to make sure it matched what I knew, I just figured it would save me a lot of typing. lol I can't say that I recommend or don't recommend anything else that author may have posted but this one was a good one. Glad it helped. 
