Genealogy / Need help with anglicized Polish sir name, Alexander [4]

My grandparents came over to American in the early 1900's. And when they got her they changed their name to Alexander. I would like to find their original name. I have looked in the US Census files and find no Alexander's before 1930. So I think that they used their Polish name on the way over. But changed it sortly after arriving in the USA. Can any one help with this..? Thank You Very Much... Tinker