My tank is a 20 gallon and i started off with a undergravel with two riser tubes and air stone... there ended up being hardly any suction from this air stone. A lot of horrible waste started gathering under the gravel, but unknown to me, until i came to the forum and it was suggested I get powerheads to put on my risers. I did, and this unsurfaced an amazing amount of waste from beneath my gravel filter. My advice to you would be to switch now, just get a powerhead to put on that one riser (u dont need a second riser). You will thank me in the future. Plus it is a bit more silent than a air pump, and also creates current for better oxygen in your tank. Just some advice :)
It looks great! Generally things like this look best when they aren't symmetrical. Maybe create a little imbalance and see how that results. You can still have your ruins decor as the "focal point", just not in the center of the tank. Play with it, maybe have two focal points. One off to one side that is devoted to plants with like colors clumped together, and the other point (the ruins) off to the other side a bit, but still with some plants on that side too. Also, maybe a little ground cover to add depth.
