Okay, that’s encouraging that at least your female Hippocampus kuda is not having buoyancy problems, Jamie, and it is good to hear that she was being more active this morning and swimming around the bottom of the tank.
Yes, if your Biocube is well-established and has an abundant population of copepods, amphipods, and meiofauna, it’s certainly possible that your female is grazing on live prey in the aquarium between meals, and that this accounts for her lack of interest in frozen Mysis, especially if you have seen her actively hunting and searching around the bottom for pods. So if her belly rings and abdomen are not pinched in or sunken in, and she has a lack of appetite, it could be that your female is scrounging up enough of the nutritious copepods and amphipods to keep her satisfied. Seahorses have excellent visual acuity under low light conditions and certain species (e.g., H. comes, H. ingens) have adopted nocturnal habits in order to escape heavy fishing pressure during the day in the wild, so it’s even possible that your female could be a secretive feeder that prefers to do most of her pod hunting after dark, when you aren’t around to observe her, Jamie.
A good way you can doublecheck to see if your female is getting enough to eat on a daily basis, even if she is feeding secretively, is to examine her fecal pellets. If the fecal pellets she is producing have not changed in quantity or appearance, you can be assured she is getting plenty to eat. As long as she is eliminating well-formed feces, that’s a pretty good indication that your female is getting plenty to eat, so if she hasn’t been scarfing up the frozen Mysis at all lately, it’s safe to assume that she has been dining on the pod population in the aquarium, just as you suspect. But beware if she starts producing white, stringy feces, or no feces at all, rather than her usual well-formed feces — those pale, stringy feces are often a sign of a seahorse that is underfed and not getting enough nourishment (or an indication of a seahorse with intestinal parasites, which could also account for a loss of appetite).
So here’s what I would like you to do for the time being, Jamie: maintain the extra aeration and stay on top of the water changes just as you have been doing but also keep a very close eye on your female for any kind of fecal production. If she is not producing feces of any kind, or if she is producing white stringy, mucoid feces, she may need further treatment.
If she still looks plump and well fed, yet she isn’t eating and is not producing feces at all, it’s also possible that she could be constipated or perhaps even egg bound. So let me know about her fecal production tomorrow or the next day and we can proceed accordingly…
Here’s hoping that she has simply developed into a secretive feeder and is getting her fill of copepods and amphipods on the sly.