I dunno what the tank height is on that... but the best size is around 3x the adult size of the horse. many readily availble horses need around 24 inches... a regular old 29 gallon works perfect for a pair or two.
to breed horses, they will breed in tank, but the babies must be taken out and maintained in thier own setup... do research on syngnathid.org and seahorse.org for all of your questions!!!