Why so little rock? Should be close to a lbs per gallon. Rock provides the surface area that nitrifying bacteria lives on.... more surface area means more bacteria which is good for the tank. Rock also provides hiding spaces for fish, and provides breeding ground for micro organisms.
Would suggest that your tank needs more rock, and at least one powerhead, 2 would be better. Please google "the berlin method", this explains how rocks and flow are the biofilter of a salt tank.
The tank needs a source of ammonia to start the cycle, otherwise the bacteria has no source of fuel. Even a pinch of fish food will help, but its very slow. Best is to buy a bottle of ammonia and add a few drops.