I would cut down to half a cube daily, and i would remove the crushed coral from your fuge. You dont need any substrate in there anyways.
I also think that is one of the crappier skimmers out there, but im not 100% sure on that.
Also, brine has zero nutritional value so i would fine some other stuff to feed them with the mysid. I would rotate through shrimp, scallops, squid, etc. Or there are some really nice mixed up stuff, like rod's food. Petco/petsmart are good places to get food.
Also, do you have any tangs or angels? They should be getting dried seaweed as well.