Hi Martha, I'm not completely sure what you're asking, or what you mean by a 50/50 starter. The hydration of this recipe as written is about 71-72%, assuming you're using an 100% hydration starter (which is composed of 113g each of flour and water). Are you considered substituting a stiff starter, or a starter that is fed with half whole wheat flour and half all-purpose flour? For more efficient troubleshooting you might want to consider giving our Baker's Hotline a call at 855-371-2253. We're here M-F from 9am-9pm EST, and Saturday and Sunday from 9am-5pm EST. We'd love to help you figure this out! 

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