With 18x turnover you can make a collection of the sun corals and their relatives: different colors and shapes.
I really like gorgonian Swiftia kofoidi (flaming tangerine orange in good cross light, plain orange when you see it LFS, thin branched, the polyps are same color as the body, NOT white. Swiftia excerta had red polyps on orange body). I'm not sure if 18x will be enough, but could be enough.
Others recommended Menella, different colors.
Red whip coral with very thin branches and minuscule white polyps on the sides of the branches (real pain to make photos) was very hardy for me so far, regenerated fast, tolerated a low flow area for a while. Possibly Elisella or Leptogorgia. You will need the small food, young fry food sized maybe.

Pardon the mess, still struggling with my tanks.
Scleronephthya will require much higher flow and more feeding, I still don't know reliable routine for it.
Suns collection will be the safest bet, these 3 gorgonians - next, and with other - more work and observations to correct the routine of keeping.
HTH