yes, its exactly like cotton wool,that must be the stuff.not familiar with the brand, but i think that's probably filter floss (does it look like cotton woll?) in which case, yes it should clear up the fine particles, put it in the last layer of the eheim.
while most filter media say's it needs replacing regularly but actually doesnt, filter floss does actually need slinging when it gets full of mank.
tip for next time, buy un branded pond filter floss, it's the same stuff but you get a massive bag for about £2/3