White things

[Sami95]

Does anyone know what are those white things in the water anf how to fix it?

 

[Abaddon]

If it doesn't move on its own, it's probably just debris. Maybe your filter sponge/media isn't dense enough and that's why it's letting these particles through. It could also be the result of the substrate being stirred up, either by you or the fish. If it moves, it could be any number of critters that inhabit aquariums (most probably cyclops - they're harmless and the fish will happily snack on them).