first off, you dont need 1lb per gallon and i think it's a silly suggestion or rule... that leads to rock walls that are ugly, lower flow, and more dead spots.
now, i really like the island look you got going, i'd just build up those 3 island so they are bigger, but if you keep them as such it will be very cool for the fish to be able to swim around and check out the other areas.
only thing i dont like, is it looks like you have 20K on the ends and a 10K in the middle.