I heard that to about the urchins, In my case I decided that at 6 inches a day move from right to left in the tank I had to take drastic actions. I added emerald crabs, the yellow tank seemed to eat everything but it at least he didn't even help after I hand pulled everything I could see.
Now in my sump I have it but it has never grown an inch in a year. I have low lighting in there, but my nitrates and phosphorous is zero or very very low. I also use those phorsphorous removing pellets in a hang on filter. When I added that my algea problems pretty much disappeared, and that may also help to slow the kelp growth. I would just be careful, I seen many tanks that a little was added and before you know it, it has covered everything so thick it could have been sold asa cha cha chea tank. It grow right over polyps and corals too which blocks there light.
Anybody else see tanks follow this scenerio?
CG