It certainly does sound like your Hippocampus reidi are thriving in your reef tank. Those prancing, dancelike displays they have been performing are preliminary stages of courtship known as the "Parallel Promenade" and the "Carousel Dance," as described below:
Dancing (Carousel or Maypole).
These are the traditional dancelike displays most people associate with seahorses. They are seen in some form in the majority of seahorse species and dancing dominates the early phases of courtship in the greater seahorses (Vincent, 1990), which do much more of this wondrous underwater waltzing than the dwarf breeds.
Seahorses dance side by side and maintain a typical posture throughout these formal displays. They hold their bodies fully erect with perfect posture, tuck their heads, and conduct themselves with great dignity as they proceed, like ballroom dancers arrayed in tuxedos and formal gowns. The result is a graceful undersea ballet in which the partners grasp a common holdfast with their tails and slowly circle around it in full courtship regalia with all the elegance they can muster (Vincent, 1990). The pair stays in perfect unison as they perform this circling dance in all their finery. Their rigid posture and bright colors irresistibly remind anyone who witnesses this display of the pairs of painted ponies and stately steeds that circle ceaselessly around a merry-go-round at the amusement park. Small wonder then that the researchers who first observed this behavior dubbed it "the Carousel dance."
Sometimes a pair begins carouseling atop a tall hitching post and spiral slowly downward until they reach the bottom again (Vincent, 1990). This lovely variation of the Carousel dance is known as the Maypole dance for obvious reasons. Together these dances play an integral role in pair formation and daily greetings for most tropical seahorses (Vincent, 1990).
Periodically the prospective partners will interrupt their passionate pas-de-deus long enough to move from one holdfast to another. They do not discontinue their courtship displays when they are on the move, as you might expect. Rather they simply switch from carouseling to a different type of dancing that’s better suited for covering ground. This is a type of highly stylized, side-by-side synchronized swimming known as the Parallel Promenade.
When promenading this way, the graceful movement of the seahorses is best described as prancing. The courting couple maintains precisely the same posture and carry themselves exactly the same way as four-legged horses do when prancing. That is, their bodies are erect with their heads held high, but inclined downwards, so as to keep their chins, errr — their snouts tucked tightly against their necks (Vincent, 1990). The pair swims side by side, facing the same direction, in tight parallel formation as they move from one hitching post to the next (Vincent, 1990). They travel in tandem as if harnessed together as a team. Their tails are often intertwined when they promenade, looking for all the world like a young couple shyly holding hands as they stroll the boardwalk.
Just occasionally, the male Tilts toward the female as they promenade, as if drawn irresistibly toward his partner (Vincent, 1990). If carried far enough, the tilt may become a tremor and then a sideways trembling, and if the female actively cooperates, an impromptu round of reciprocal quivering may result, particularly in miniature species. Eventually the overexcited male will regain his composure, and the promenade will proceed to its intended destination, where more Carousel dancing will ensue.
Like the other dances, promenading is an early stage of courtship seen primarily in large tropical seahorses (Vincent, 1990).
So it certainly sounds like you’re H. reidi are in the process of pairing up, Nigel. When they are getting serious about mating, the male will begin performing his vigorous pouch displays (Ballooning and Pumping) and the female will respond by nodding her head, pointing her snout towards the surface, and stretching upwards on the tip of her tail. That’s a sure sign that the couple is ready for the copulatory rise and transfer of the eggs.
Best of luck with your pair of reidi, Nigel! Once they begin breeding, they’ll turn out brood after brood every 14-21 days with clock like regularity.