I was using As I Am Coconut Cowash and started developing dry scalp and itching. Then it occurred to me wait a minute, I never had "dry scalp" before CG. I never had oily scalp either. I was just normal. Then I found out a preservative in my cowash caused itchy scalp:
Itchy Scalp Causes: Preservatives in Hair Products
And I wised up. Stopped co-washing the scalp completely. I wash my hair every other day so what I started doing was a tea tree oil treatment one day, straight up water washing another, and on the third wash day of the week I'd low poo with a super gentle cleanser so as to not dry out my hair. (Shea Moisture's Moisture Retention Shampoo or their Yucca Baobab Shampoo. I love both. Light lather, and neither strips my hair.)
The reason I used tea tree oil is because I know it's good for regulating sebum and thus preventing buildup. What I would do is take about six q-tips and dip either side into tea tree oil. Then really fast, I'd dip the ends on a little dixie cup filled shallowly with water to dilute the oil. Then I'd apply directly to the scalp and give myself a massage treatment with smooth circular motions. The twelve ends of the q-tips are roughly enough to cover my whole head I've found. Then I got in the shower and rinsed and co-washed my hair, yes, but not the scalp. I'd apply conditioner a few inches past my roots to avoid the scalp.
But then I found Trader Joe's Tea Tree tingle conditioner. It is a godsend. I love it. It has no preservatives that cause itchy scalp and lots of delicious clarifying oils that cleanse the hair while it moisturizes. I can co-wash with this, I've found, and have no buildup at all or itching. So here's what I do now. Say today is Sunday and I'd wash my hair today: I'd co-wash the scalp with Trader Joe's tea tree tingle. On Tuesday I'd do a tea tree treatment then water rinse. On Thursday I'd use either of my low poos.
Also those low poos are so super gentle I think they'd be safe for you to use more than once a week if you like. Also I have to agree 100% with Korkscrew. Clarifying your hair with a straight up sulfate shampoo once in a while is not going to hurt it. You can always do a pre poo where you slather your hair in protective oils (olive, coconut) and conditioner an hour before you shampoo to protect your hair from getting stripped. A good silicone free shampoo that's super cheap you might use for clarifying is Suave Naturals Coconut. $1 at the drugstore. Sulfates are not the devil. And you shouldn't have to suffer a dry itchy scalp or product buildup to have well moisturized curly hair. You do what's right for you.
Experiment and you'll find a balance. Maybe you can do your giovanni tea tree shampoo twice a week and deep treat after you shampoo. Or do a mini deep treatment. That's where I put a little bit of leave in conditioner in my hair and throw on a shower cap and sleep. (This is when I shower at night.) In the morning I rinse and style. Having slept with conditioner my hair is super soft come morning.