Do they even eat chaeto in their diet? I know nothing about seahorses, except this odds of anything living would increase by giving them the right food, right? I did a two second internet search on food and found the following article:
Seahorse Foods and Feeding
A brief overview of what and how to feed your seahorses.
by Tamara Weiss
Seahorses are ambush predators, feeding primarily on crustaceans, mostly shrimp. In their wild state, most seahorses only eat live food. (Although H. capensis is an exception and known to feed on dead food in the wild). In our aquariums, Wild Caught specimens often don't recognize many food items offer that are not from their natural environment. This includes dead food, which they just don't see as food unless trained to make the switch.
Captive reared seahorse, on the other hand, are almost always willing to accept frozen. It seems as though being in captivity makes them more willing to try new foods. Even those captive reared seahorses not previously fed frozen make the switch almost immediately in most cases.
It is ideal to offer seahorses a variety of foods - in the wild, they would not eat only one food source, so in captivity they shouldn't be expected to. Varying their diet allows for a more complete nutritional profile, as well as providing mental stimulation which they often lack by only feeding one food type.
When feeding, whether live or frozen foods, its best to offer food that originated from a marine environment. Marine animals are rich in Highly Unsaturated Fatty Acids (HUFAs) that freshwater organisms lack or have in the wrong concentrations. The HUFAs are produced by phytoplankton, base of the marine food chain so all marine organisms are dependant on them in some way. Freshwater animals fed can be fed to marine animals, but they need to be enriched with different products containing the necessary fatty acids, such as Selco, or Ocean Rider Vibrance.
The exception to this rule is Brine shrimp, while they are technical marine, coming from a saline environment, their ecosystem is much different than the ocean, and therefore do not have the HUFA's of other marine
animals.
http://www.seahorse.org/library/articles/SeahorseFoods.php
I am sure there is a ton of information out there on proper foods, but it would seem cruel to experiment with things that are not in their normal diet? My 2 cents....