Ok thank you ill research those but some of my corals wont stay glued no matter how much I glue them.I would skip the tang and go for an urchin. My pincushion goes to town on it (though even these might get too big for a 20 and you will have to supplement with nori).
Manually removing the big clumps and adding some money cowries might do the trick as well. They have the added benefit of:
a. Looking awesome
b. Being Seemingly not interesting to hungry hermit crabs due to shell shape
c. Unlike their bigger cowrie cousins are completely reef safe
(Also manually removing big clumps will serve as a nutrient export mechanism which will help the underlying problem)


