What is this stuff floating around in my res?

Saw some weird stuff floating around in my res bucket today.
2 girls, Start of 3rd week since sprouting
Temp: 72.5F (was 68 in the morning)
Nutes: 2.5ml/g each GH Flora series
pH: 5.9, stable since last night
Water level, stable
Added 5ml of 34% H2O2 this morning
Air stones in each grow bucket and water entering via waterfall

It's not slimy at all, bucket walls in grow and res buckets all squeaky clean too. Grabbed one and it felt a bit rough, like some dust or lint. I inspected my roots, which are just poking out of the net pots about 3-4" now, and they're all nice and white. I did find ONE of these things dangling from the very tip of one of the root tips though (the one at the bottom of the cup). Might have just been caught while circulating. It doesn't appear to be organic matter, but I am not sure.

I just added a few drops of regular bleach to the measuring cup and let it sit for few minutes. All that did was cause all the things to float to the top and make the cup walls exhibit a bunch of bubbles (prolly the chlorine reacting to the H2O2).

Found some light leaks through the net pots. Covered the tops with foil and made sure there were no more light leaks. Hope that was just some algae and the problem is now solved.

in case anyone is interested in an update...

followup to what I did 9hrs ago in addition to fixing the light leak...
- placed the girls in a smaller bucket w/ 5ml/gal 0.03% chlorine solution (homemade uc roots) to rinse off whatever was stuck on the roots
- much more of that gunk was stuck to the sides and bottom of the bucket
- irradiated the grow bucket for a few min w/ a 5w uvc bulb
- stirred everything and the gunk easily lifted off the sides of the bucket
- UVC again for a few min
- replaced the girls
- repeat in 2nd bucket.
- threw some ice packs into res to lower temps (now at 68.5)

Checked this morning and there is a significant reduction in the amount of gunk floating around. Maybe only a few larger clumps. Rinsed roots again using a fresh chlorine solution (same temp water) and slipped some 75 micron mesh filter bags over the waterfall entry to catch whatever leftover remnants that are still circulating. Hoping this is the end of it.

Oh, and ppm dropped from 420 to 340, ph stayed the same at 5.9, and water level was down about 1/4-1/2".