To any others who are considering it: regardless of the temps seahorses may be found in naturally, hobbyists have found that greater success is had when seahorses are kept 74 degrees or below when in a tank. Tests have shown that a common bacteria of seahorses is able to multiple and mutate at a much faster rate at temps above 74 degrees.
Seahorses are also not the strongest of swimmers (although there is a temperate species that is a stronger swimmer, it needs to be kept 64 degrees or below and therefore is not native to a reef habitat) and need to be kept from corals with a strong sting and those inverts that consume fish. There are numerous fish that will eat, bite, or pick at a seahorse (including lawnmower blennies), and most fish will out compete a seahorse for food. Seahorses need to eat a lot and frequently due to their inefficent alimentary tract. Thus, they create a lot of waste. Fleet fish can "spook" a seahorse, causing stress and even causing the seahorse to go off its food.
In general, seahorses and reef tanks are not a good match.