The older serums that exist are bullshit. They are mixed in water and then it becomes creatinine (spelling? dont know the english word) and it becomes useless. It needs a water free solution to be stable (because water changes the molecul(spelling again) and makes it different). New stuff is being developed, but i wont try that shit.
Anyways, german Creatine is by far the best! where it´s made has bullshit to do with the quality!
I personally use Optimum Nutrition´s Creapure powder, works fine.
good luck!