Someone here mentioned that using 1tsp ACV per cup of water makes the pH of the solution match the natural pH of hair. So, at that concentration, it could be safely used every wash, since it would normalize the hair's pH. I prefer the results I get from using 1 Tbsp per cup of water in my once a week ACV rinse though. I cowash, rinse, apply ACV rinse (and leave it in), apply my RO, then rinse and proceed normally with the rest of my routine.
CG since 11/2011
2c /3a F /Mii, low porosity

Go To Products /Routine:
Clarifying: Suave Essentials Strawberry
Low Poo: Renpure Luxurious Argan Oil
CO: Suave Essentials Strawberry, V05 Kiwi Lime
RO /LI: Tresemme Perfectly (un)Done, Cure Care, V05 Kiwi Lime Squeeze, Suave Essentials Strawberry, Renpure Brazilian Keratin (old formula)
Stylers: LALSG, AIF, HETT, Suave Professionals Firm Control
PT: IAGirl's as needed