I need to amend my my last response regarding the corals you are patiently waiting to add to your seahorse tank. As Leslie Leddo reminded me, the elephant your mushroom coral you mentioned is NOT safe to keep with seahorses or other small fishes!
As I mentioned before, soft corals have very little stinging ability and generally make good choices for a modified mini reef that will include seahorses. This includes most zoanthids and mushroom anemones (corallimorpharians) in general. However, as Charles Delbeek cautions, "One notable exception is the elephant ear mushroom anemone (Amplexidiscus fenestrafer). This animal is an active feeder on small fish and will envelope them whole with its mantle then slowly digest them by extruding its digestive filaments into the space created. No small fish are safe with these animals in the tank."
So you will need to exclude the elephant ear mushroom coral from your seahorse tank and find another home for that particular specimen, Carrie. Some of the soft corals that generally do well with seahorses in a low/moderate light, low-to-moderate flow reef tank with PC lighting are listed below, and would make good substitutes for the elephant ear:
Finger Leather Coral (Lobophyton sp.)
Flower Tree Coral – Red / Orange, (Scleronephthya spp.)
aka: Scleronephthya Strawberry Coral, or Pink or Orange Cauliflower Coral
Christmas Tree Coral (Sphaerella spp.)
aka: the Medusa Coral, Snake Locks Coral, or French Tickler
Cauliflower Colt Coral (Cladiella sp.)
aka: Colt Coral, Soft Finger Leather Coral, Seaman’s Hands or Blushing Coral.
Toadstool Mushroom Leather Coral (Sarcophyton sp.)
aka: Sarcophyton Coral, Mushroom, Leather, or Trough Corals.
Bullseye Mushroom Coral (Rhodactis inchoata)
aka: Tonga Blue Mushroom, Small Elephant Ear Mushroom (rarely)
Clove Polyps (Clavularia sp.)
Stick Polyp (Parazoanthus swiftii)
Green Daisy Polyps (Clavularia sp.), Indonesia
Orange & Green Colony Button Polyps (Zooanthus sp.), Fiji
Pulsing Corals (Xenia spp.)
Red Ricordea (Ricordea sp.), Indonesia, occasionally Solomon Islands
Lavender Hairy Mushroom (Actinodiscus sp.), Tonga
Pimpled Mushroom (Discosoma sp.), Indonesia
Other low light corals that should be suitable include genera such as Cynarina, Scolymia and Trachyphyllia, as well as non-photosynthetic gorgonians such as Subergorgia and Didogorgia, and perhaps wire corals such as Cirripathes spp.. However, supplemental feedings of zooplankton may be required to maintain these corals in good health.
The small polyped stony (SPS) corals generally have weak stings that should not pose a threat to seahorses. Depending on conditions in the tank, SPS corals such as Acropora, Montipora, Pocillipora, Porities, Seriatopora and Stylophora can be tried at your discretion.
Best of luck with your new seahorse tank, Carrie, and the seahorse-save corals you eventually add to it!