You can try it and see how you feel. Grapefruit Seed Extract has a bit more of the anti-parasitic and anti-bacterial potency than Caprylic. For a second phase, it's usually fine as the first level anti-fungal has taken the yeast levels down. Doing GSE right off at first means you might have a stronger reaction, depending your level of fungus/ bacteria/ parasites and your sensitivity.
As long as you have no contraindications (like certain medications), and you listen to your body and back off if needed, it may work well for you. Here's a post about dealing with die off that might be helpful.
Take good care,