Something else to think about is reef tanks don't have to be 78+ to thrive. I keep mine cooler in the winter 75-77 which is still high for a seahorse tank, but much more doable with an over sized UV and regular water changes.
As I said, I plan on lowering the reef temp, just not below 76. An oversized UV will increase heat. I think a 15 watt in line with the seahorse tank supply will work just fine. It will have about 200-300 GPH going through it. While this is undersized for the entire system, it is about right for the seahorse tank. The flow is kinda up in the air right now as I haven't calculated the dosage required yet. This goal will be to provide the UV exposure required to kill Vibrio sp. bacteria and limit the population of others without adding heat to the water.
I see no reason why 76-78 is not a responsible temperature for H.redi seahorses when the following conditions are met:
1. Stable water conditions are maintained.
0 ammonia, nitrite, and nitrate < 5 ppm (< 2 ppm in my tank)
Temperature stability +/- 1 F
Low TOC/High ORP
Stable water chemistry particularly salinity
2. Stress reducing environment
Low flow resting/hiding areas
Placement of tank in low traffic area
STABILITY
3. Bacteria and other pathogen control
UV, ozone, skimming, etc.
4. Increased flow and a clean-up crew to remove uneaten food and waste
Sadly, I'm not saying I won't lost a seahorse while learning to care for them, but as far as I can tell from the reading I've done, neither can most regardless of the method they use.