[piercho]

Asparagopsis is a tough one, sorry. You may find a grazer (Diadema?) but IMO it won't graze Asparagopsis preferentially. IME, competetive control from an optimized vegetative filter and manual removal can be an effective, long-term control for Asparagopsis. A combination of scrapping (Diadema urchin) and rasping (Combtooth tang) grazers helps prevent Asparagopis and other detritus-trapping algae from gaining a foothold on rock once they are reasonably controlled.

I don't know if Asparagopsis survives solely by advection, or if nutrients from the substrate or trapped detritus play a significant role in its growth. Its possible that Asparagopsis gets some nutrients from the sand or rock it grows over. Also, IMO Asparagopsis probably gets some nutrients from trapping detritus in its fine filaments. While manual removal no doubt sends small fragments all over the tank, once its well-establish IMO there is no reason not to manually remove it as frequently as you can.

In competetive control you offer a preferential environment for uptake in a vegetative filter - which means better water circulation and higher intensity light in the filter than in the tank. Even then, its a slow fight, IME. There may be other methods of control for Asparagopsis that work better than this, but this has been my main means of control for display tank algae, including Asparagopsis.

If you can tolerate a Diadema urchin in you tank, a combination of a Diadema urchin and a combtooth tang has worked best for me for general algae control. Diadema grazes the rock very hard, down to bare white carbonate. Combtooths like Koles then will work over the bare rock, rasping away detritus and new growths of algae. Eventually the rock does start to accumulate algae the Kole tang won't remove, but sooner or later the Diadema passes over that area again, scrapping it back down to bare bone. Diadema aren't entirely benign, I've had them start sampling coral as they get large and even had one occurence where a Diadema trapped a small sleeping fish and was eating it. They also knock off any small object that isn't solidly secured to the rock, and they grow large very fast. But, one heck of a grazer.

I don't have a reference or experience that boosting carbonate alk, hyposalinity, or hypersalintiy are effective for Asparagopsis. It doesn't mean that one of them isn't effective. Boosting carbonate alk may help slow down non-calcified algae by shifting production to calcified algae like coralines and Halimeda.