Thank you all of you for answers.
My experience with is that this particular video is tanken in a small 12 liter tank in which I at the same time discovered 6 or more different size fry, from 1 cm to 0.5 cm, – and I dont think the ‘infusoria’ has just arrived yesterday. So I would conclude that it actually is not a problem – at least not a big one – to the small fry.
I must admit I see these kind of ‘clouds’ of moving particles sometimes in my paro-tanks, – sometimes they are much much smaller and might look a little bit like vineager eels, (but they are not) and sometime it like in the video – bigger and they move in ‘clouds’ – I saw today, that one such small cloud formed in front of the tank, looking like a tiny spiral or something ..
The fry swimm now in and around it, but dont seem to eat it.
I actually have tried lately to grow infusoria (with a green salat leaf in water, and pouring it into the tanks) – and after such a treatment I do now expect that there will be – also visible – infusoria. I do this because I often have these undetected small fry, and I never know when to feed them or not, so basicly I try to keep some tanks really ‘ready’ no matter what, concerning food supply for small fry.
But I had not done this to the ‘video-tank’, – but as I said this tank was really old and overgrown, and probably with a lot of old leaves that has rotten ..