I have to agree, 5nl is nittier than 10nl is at pokerstars
People say they are imagining it, but I believe it to be true.
It's most definetly beatable though, once you learn to beat the nits and just pound on them each street.
I belive the reason for the nits at 5nl is because, the minimim deposit on stars is $10.00. Therefore, your recreational "fish" will highly likely go straight to 10nl, as opposed to think "Oh, I have 2 buy-ins for 5nl" They wont think on this level and will just go play at 10nl.
I find there are a TON of grinders at 5nl, who have likely read forums, followed stratergy etc and have literally grinded from 2nl, currently at 5nl but nit vs nit constantly etc..
Just start opening up more vs the nits and still value bet your strong hands, but take different "standard" lines vs the nits who will likely fold unless they have a monster themselves.