Somehow I missed this thread. I have a few cautions about the set up that you are planning. The biggest is temperature...seahorses do best in water temperatures under 75°F. Some folks have kept seahorses in temperatures that are higher but very few have done it successfully long term. With your smaller seahorse tank being plumbed into the larger reef tank, the seahorse tank will undoubtedly be 78° or higher. The only way to keep seahorses in those temperatures long term is to only feed live food, gut loaded mysis, or ghost shrimp and gut loaded live brine shrimp.
Glad to share some of the pitfalls that I experienced.
Don't agree on the temperature information, here is an article that states 76-78. This has loads of great info, http://www.advancedaquarist.com/2004/12/fish2.
I respect your choice to disagree and that is fine. I will say that that article was written in 2004 and that captive bred seahorses were fairly new then. Before CB seahorses, folks kept wild caught seahorses and fed them live food in aquariums that were at reef temperatures. Those ponies did not get bacterial infections of the gut because their food was living. Now that CB seahorses eat frozen mysis that has changed. Seahorses are messy eaters and tend to let their food drift away and at times get caught in the coral, rocks or macro algae. In temperatures over 74° pathogenic bacteria like vibrio are fueled by the decaying food. For every degree above 74° they reproduce exponentially. Since seahorses lack immune response in their digestive tracts they can get sick and succumb quickly if they eat some of that decaying mysis. You can check my info with Ocean Rider's tech, Pete Giwonja who is an expert on seahorses.
You may keep your seahorses at whatever works for you. I keep mine in the low 70s.
