75 percent should work fine, that's what I used. Interesting they're watering it down in the U.S. I wonder why. At least it's still relatively inexpensive there, unlike here in UK, where it's the equivalent of about 5USD/bottle. Hard to find here as well. I have to go to Amazon UK because it's not available in pharmacies or supermarkets. Weird! I had a problem with adulterated product too but finally managed to find a reliable supplier.