Incoming tide almost always has the best visibility, unless there is a very heavy surf just ouside, when visibility is bad no matter when. The absolute best visibility, all things being equal, is during the half hour or so around peak high when there is almost no tidal movement and a great deal of precipitate drops out of the water column.
Rain can make an outgoing tide especially dirty because of all the stuff washed into the water upstream. The effect is less pronounced the closer to the ocean you are.
There is usually better visibility close to shore if the near shore area is partially protected from currents by structure. Sandy bottoms tend to offer better visibility than muddy bottoms, another factor that tends to make it more clear as you get closer to the ocean. Sand drops out of suspension quickly.
As temps drop significantly below 60F the seahorses (Hippocampus erectus) will adopt a tight 'comma'curl, head tucked tightly against the body, tail fully curled, breathing very slowly, not swimming or eating, essentially dormant, drifting with the tides.
There are probably two populations, native seahorses and Gulf Stream strays. The locals seem to survive the winter, at least some do, while the strays, though the same species, don't make it. Research on this phenomenon has been going on at Woods Hole for decades. I've found live completely dormant overwintering seahorses in back bays, and some have come up from lobster traps in mid-winter in New England.
I have one seahorse at home I picked up as a little tiny thing last year in Manasquan Inlet. I was impressed by the tireless zeal with which she searched for food, carefully examining every object with microscopic intensity, looking in every possible nook and cranny as each eye focused independently. She is doing quite well 15 months later, almost full grown, exhibiting the same relentless hunting strategy in a large heavily overgrown aquarium she shares with two large fish and no competitors for the profusion of small life forms that scurry among the many coral rocks and hide in the coral gravel.
Other than this exception I don't collect seahorses at all. Butterflys, Angels, Spiny Puffers, Bigeyes, Damsels, Lookdowns, yes, I'm happy to share them with friends and small shops, but never seahorses. The others all will die anyway, are dying now, in fact, as the waters grow cold, but the seahorses are too rare and fragile to put into the hands of the average aquarist.