another thing you have to keep in mind is that seahorses are vertically oriented fish and do better in taller tanks, especially if you obtain a mated pair. They will move up and down through the water column, each morning to strengthen their pair bond, not to mention to search your lr for food (copeopods, amphipods, etc). MY MOM HAs the same problem in the fuge that filters her 135, she wants to put some dwarf seahorses Hippocampus zoasterae, but it is so dense with caulerpa, and so "vertically challenge" ha that they wouldnt have any room to move around!
i would not reccommend it, for the sake of the horses!
good luck
jon