How about some of the sexually dimorphic Genicanthus? You know that I love 'em.
They will try and spawn in my 240 and 120... not very well, though.
Have you considered 150W HQI instead of the kessils? Just curious. Some people think that 150W is not that much, but they are no joke. My apologies if you have used them before. I don't think that you would need as many as you would Kessils so the wattage might be the same. Anyway, I was just curious since lighting is the main reason that I don't have the 1200G here and set up - so wanting to learn and appreciate your thoughts.
If you want to do mangroves big-time, plan your top off to act like rain to shower the mangroves with RO/DI... and fill the tank at the same time.