Hi, I hope you don't mind some constructive criticisms
Not rules, just suggestions. ok, the 3 rock formations look really unnatural and symmetrical. You want to employ the rule of thirds.. with a strong foreground and a mild "toned down" background. Your rock formations are very predictable.. it reminds me of those orange cones on the road. 1......2.......3
You want something that "builds up".. start with a low rock that eventually leads to a pile of rocks. In photography, this is similar to "leading lines" which is very pleasant to look at. Remember, you don't want symmetry! Nature is very random.
And finally, with a shallow tank like that, you want to "get low" as much as possible to allow swimming room, growth, and most importantly, flow on top of the structure. I'm personally not a fan of caves, but that's just me.
Again, these are not rules... just humble suggestions. Aquascaping is an art, and there's no rules in art - just guides
