Very tiny white bugs (crustaceans?), hoping someone can identity them and advise

[DaPrawf]

My betta recently developed vertical hang. I moved him to a quarantine tank and gave him a one week treatment of Maracyn II. By the end of the week, he has recovered nicely. To prepare his home (a 7 gallon cube) I had treated it with both Maracyn and Maracyn II. I then sucked out as much of the water as I could. My substrate was UNS Controsoil (am I allowed to mention brand names). I wanted to brighten things up a little, so I added a later of thoroughly washed CaribSea Super Naturals Peace River substrate. Refilled the aquarium with fresh dechlorinated water. Added Stability to restart the nitrogen cycle. The next morning I checked the tank parameters and I had a serious ammonia spike and a mass extinction of cherry shrimp. I pulled out all the plants and ornaments. I removed about 30 dead shrimp.  But I noticed these little white bugs that look sort of like crustaceans of some sort had survived. Anyway, I tossed the old plants, cleaned all the ornaments, and when the nitrogen cycle restarted, I put the betta back in his tank with new plants. He's doing great but I still have these little white bugs. I thought maybe they were shrimp babies that had somehow survived the big dieoff but they're not getting bigger. The only change prior to the appearance of these little bugs was adding the Maracyn and the Caribsea substrate. Any idea what they are? Should I worry about them? If so, how do I deal with them? Thanks.

Edited October 21, 2023 by DaPrawf
Added washing the substrate.

[jwcarlson]

Scuds

[Guppysnail]

Amphipods aka scuds are harmless cleanup crew and fish food. As long as you are not overfeeding and keep the tank clean they will not overpopulate. They are incredibly fun to watch.