I suspect this is a fish parasite of some sort, and posted in another forum, but on the off chance it is something related to things that live in plants...
And I am really new to aquariums, and so worry for anything unusual....
I noticed what looked like rapidly swirling hair, and then realized it was some kind of free swimming worm. I only noticed as it was up near the light.
I scooped it out in a plastic cup where it is extremely actively swimming at the top of the water, vertical in orientation. it is about 8 mm long give or take, so this is a rather extreme blowup, the horizontal lines are the top of the water in the cup.
Tank details below. I have not feed any live food. I have fed packaged, freeze dried bloodworms, which this looks remotely like, but not all that much.
I am currently using a heat-only treatment for ich, on about day 7 at 88F, most signs are gone from the one fish that had it, everyone else was/is healthy looking. I have seen no signs of anything like this hanging on fish.
Other recent event is I did a filter clean for the first time 2 days ago, and it's very possible something got washed out that was living in it. It was not very dirty, and I very lightly rinsed the spongy media in its own water. It's a fluval 306.
Ghost shrimp are pregnant and giving off larvae but this doesn't look like any photos I've seen (and I assume the fish are eating them before I see them).
Is this a sign of some parasite I should be concerned about? This particular one is out of the tank of course, but it seems unlikely to be the only one, regardless of what it is.
Tank: 45G, new-ish, 2 months old, cycled in first month. Chemistry normal (ammonia 0, nitrite 0, nitrates 5-20 ppm, about 10ppm now, KG 5.5, GH 9, ph 7.6 (slowing reducing from about 8.0 with WC's).
Planted lightly on gravel/ecco-complete, all rocks and such added at during the first two weeks or so, nothing new. Jungle val (mostly), amazon sword, crypt wendtii, anubis. No CO2, light ferts from seacheam.
Stock: 1 x raphae catfish, 1 x bristlenose pleco (tiny), 5 x tetra serpae, 5 x congo tetra, 6 x ramshorn snails (early hitchikers), 4 x nitrite snails, 10 x ghost shrinp. Latest arrivals were 2 x congo tetra and BN pleco and nerite snails about 2 weeks ago. All stock from the same nearby LFS.
Lit with Satellite LED+ 2 x 4 hrs daily.
No obvious issues with water, clear, scavengers are keeping up with light algae growth.