I don't use a preservative because I make a little bit each time. I only make about 4 to 6 ounces so it will finish quickly and then I play with the amounts (more Aleo Vera, less honey, some shea butter, etc) and I can throw it away if I notice bacteria developing (it never happened to me though, I make sure I wash the bottle with warm water and soap before I refill again). Each combination lasts me at least 3 weeks and sometimes a month and I have a lot of hair, I'm sure it would last someone with thinner or shorter hair much longer.
A Mediterranean 3b lady
In love with my curls, love love love
CG since Nov/07

Co-Wash: VO5, Tresemme naturals, Fructis naturals
Cond: Nature's Gate conditioners
Stylers: Lotions made at home with coconut oil, honey, AVG, vegetable glycerin, OO, and EO.
Gel: LA Looks sports gel for high humidity days.

Hair goal: Waist length healthy curls