If you have a numerous, active, efficient cleanup crew, then scatter feeding the frozen Mysis as you describe can work out okay, at least for a while, but it’s a risky strategy for most home hobbyists.
To me, it sounds like your ponies would take very well to target feeding the frozen Mysis by using using a Turkey baster or feeding wand to dangle a single Mysis shrimp from the very tip of the wand right in front of the snout of the seahorse you are feeding, until it slurps it up right from the baster or chases it down if it misses with its initial strike.
Once ponies get the hang of target feeding, it is then an easy matter to lead them over to one of the feeding stations so you can deposit the Mysis shrimp they have been following on the tip of your feeding wand into the feeder. And once you have trained one of the seahorses to come to the feeding station and begin feeding directly on the frozen Mysis contained in your feeding dish, the other ponies usually quickly learn from its example, and keeping your ponies well fed becomes quick and easy, just like that…
As I mentioned, scatter feeding the frozen Mysis and relying on your cleanup crew to clean up any leftovers that find their way into inaccessible areas of the aquarium can be a risky strategy for a couple of reasons. First of all, when scatter feeding frozen Mysis, it’s not only the ponies that are getting fed – it’s also the aquarium filters, which will be sucking up and eating a portion of the frozen Mysis while it’s floating freely around the aquarium. Secondly, some of the frozen Mysis can find its way into areas of the aquarium that are inaccessible to your cleanup crew as well as inaccessible to the seahorses, such as in small crevices, nooks and crannies in the rock work, or tiny recesses beneath the corals and decorations.
In either of those scenarios, the leftover frozen Mysis that gets “eaten” by the aquarium filters or that ends up out of reach to the aquarium janitors and scavengers as well as to the ponies, will begin to decompose and degrade your water quality as it breaks down. Even if this is only a small percentage of the frozen Mysis you are scatter feeding, it will make a difference over time, and deteriorating water quality is one of the primary causes of disease problems in seahorses.
Secondly, as a rule, you’ll want to prevent the frozen Mysis you’re offering to your seahorses from settling on the bottom of the aquarium, if at all possible, Bill. The substrate or bottom of the tank is where the seahorses fecal pellets and other wastes and detritus accumulates, and you don’t want your ponies to eat leftover Mysis that may have become tainted or contaminated with bacteria in this way. That can become the case all too often when leftovers find their way into inaccessible areas of the aquarium, and settle to the bottom, only to eventually be wafted out into the open again by the water currents, where the seahorses may find it and feed on the bacteria-laden Mysis, which is always undesirable. (If you think about it, that’s kind of like dropping your sandwich on the bathroom floor and then picking it up and eating it anyway – yuck!) So I’m not so sure the “3-second rule” applies in your seahorse tank any more than it does in the lavatory.
For what it’s worth, those are my thoughts on the matter, guys. Personally, I prefer to target feed my seahorses one frozen Mysid shrimp at a time to make sure each morsel gets eaten straightaway, or to train my ponies to eat the frozen Mysis I have deposited in a clean feeding dish that I keep a sterile as possible, or to take the frozen Mysis from a natural feeding station like a lush, bushy colony of red grape Caulerpa (Botryocladia).
Best wishes with all your fishes!