Sorry...old pic...The "plants" are actually the "silk" ones they used to give out in buckets of Instant Ocean.
I too wanted "something" in the tank beside fish and rocks...
Later I went to live Macros in the display tank, but have since moved them to a refugium...
Eventually the coraline started growing and adding color...a couple crabs and snails to play hide and seek with...and then another fish or two to "round out" the tank.
I also started a "Nano" Reef for more color and varity as I realized the "limitations" of an aggressive tank...Don't get me wrong, I love my "Meat Eaters" but that "type" of tank limits what you can add to it...
And on that subject...Triggers and Puffers (for the most part) are NOT good tankmates with a Lion...They tend to be attracted to the flowing fins of a Lion and may "nip" on them eventually stressing the Lion or at the very least causing him to loose his "plumage"...so be carefull there...
I have tossed afew "low light" corals (extras from my reef) in the aggressive tank and they seem to be hanging in there..