I might wash twice with the herb mixture, and give up on the SLS shampoo. I suspect that the shampoo is over cleaning, and that the herbs will perform better used on their own. You could try several washes in a row with herbs, increasing frequency at first, to see how it worked. Then once things stabilize, you could stretch out your washes again.
Also, when using herbs, I apply the mixture, let sit for 10 minutes or so (while shaving etc), massage, then rinse. Did you do it this way?
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