Unless your feeding the enrichment to live food and then feeding to the seahorses I think you are wasting your time IME.
Most of the enrichment just comes off in the water, very little actually sticks to the food, and then makes it through into the seahorses digestive system. It does add a nice little cloud they exhale through there gills after they snick something though . . .
If you want to feed them enrichments I think vitamin C is good but beta glucan is going to be your best bet. You can find the powder capsuls at most health food stores. Just feed the capsul to a bag full of brine shrimp, wait a half hour or so and then feed that live brine to your seahorses. I wouldn't feed live to often, maybe once a week or so. If you feed to much live food they start looking at the frozen food like, "Where's the live food, I'm not eating this." Then again some seahorses are actually scared of live brine, but yours being captive bred should not be, I ran into this more when working with WC reidi and comes.
I only know all of this because I tried for quite some time to figure out the enrichment thing. In the end I found I could keep very healthy seahroses longterm (5 years +) without feeding enrichments and by only ever feeding fresh water foods that contained little of the HUFA's.
Oh, since they are eating the PE, I would just feed the hikari to your reef, the seahorses need all the protein they can get, especially at there size, so a snicked hikari is a waste for them.
Sorry I'm so opinionated.
HTH