aragonite was a good choice - I'm not sure of the size of the black grains but I'm thinking most I've seen on other tanks appears to be a medium grain which is good. I love the look of black sand, have never had it but have always thought the look was awesome!
I used Fiji pink in my larger tank. I hate it. Makes a sand storm if I turn my power head on to high or if my pistol shrimp is remodeling. I used special grade in my pico tank and love it! Not to large to look ugly but not small enogmugh to get blown around.