I currently have these in plague proportions -- I had 3 newly-added neocaridina die over the weekend, and the worms seem to have exploded from the nutrients. Im not sure why the shrimp died, all parameters look (and looked) great.
I also keep this as a black-water-esque tank, so there are lots of decomposing leaves/organic matter that these worms flock to as well.
Anyway, any idea on what these are? I don't think they are actively harming anything. They are extraordinarily tiny, slightly yellow, can form little star-shaped clusters, or freely swim in dense clouds where there is low flow.
Besides ID, any idea on control measures? I actually don't feed this tank, only add leaves as needed. Im not interested in chemical treatments either
I'd be looking into why your shrimp are dying in the first place. The Worms if that's what they really are could be a symptom of a bigger problem.
Neocaridina are generally tough as nails, especially less colored ones.
But like all shrimp, they don't do well in tanks with an adverse water parameter.
You say your tank is 'blackwater-esque" You realize their native streams are moderately hard with near equal amounts of carbonate hardness and general hardness? they also prefer neutral to somewhat alkaline pH. They do adapt to softer conditions, more acidic conditions. But will never thrive or reproduce in great numbers if they're swiftly changed from their normal water conditions to one that lacks sufficient mineralization.
For your own peace of mind, pick up API's GH/KH test kit and a Total Dissolved Solids 'pen' meter. The TDS pens are cheap and even the cheap ones have temperature compensation to keep their accuracy over a wide range of temperatures.
Secondly I suspect that we're not getting the entire story on their tank. Is this a "dirted" substrate tank with organic potting soil under a gravel cap? Has it been allowed to age and cycle?
The level of organics is worrisome. Shrimp natively come from somewhat sparsely detritused streams and forage mostly on biofilm. Secondly did you completely Nitrogen cycle the tank? A Neo tank should be thoroughly cycled, tested for Ammonia, Nitrite and Nitrate. Because of their somewhat basic or alkaline water preferences, ammonia that's not converted to Nitrate will be much more toxic.
The worms you describe should not be present in "free swimming clouds". It generally means the substrate is such an organic soup that they're not enjoying living in it.
These worms in your photos are all spherical-roundish, are you sure they're not seed shrimp? Do they glide on the glass or do they move about like drunken bumblebees?
The star shaped forms are worrisome because it could be you have an infestation of Hydra, you've mistaken for worms. Hydra can be bad for both adults and juvenile shrimp.