Hmm, maybe try a deception routine with the caulerpa outbreak vs trying to fight it.
Basically, setting up a refugium with some other competing but more benign versions of caulerpa so they can strip the specific nutrient stack out of the water and starve the bad stuff out? Usually the faster the grower, the more it's sensitive to required nutrients.
I'm not entirely sure on this, but I thought caulerpa required iron and/or manganese to grow while nitrate was just dessert. Iron and manganese require replenishment from somewhere be it bad tap water, RO
in need of repair, or just plain old salt mix.
Caulerpa *will not grow* in my older 55 that I do very infrequent water changes. It will grow in my FO
tank with weekly water changes.