A little late on this one. Seahorses are notorious for having a low survival rate within captive breeding. That being said, this varies depending on the particular species that you have. One of the main reasons, just like most marine fish, is providing the correct "first" food. Doubly so with seahorses considering they lack a "true" stomach, so the nutritional value of the provided food needs to be quite high. The rearing vessel is just as important. "Kreisel" style rearing systems are generally the way to go, at least in the early stages. These allow for a steady, controlled water flow, as well as providing a system where the animals will not get caught on edges or in corners. Another benefit to these systems is that they allow for good mixing of the animals and their food. A mix of large type rotifers, artemia nauplii, and other varias copopods are used to get them to a size and condition where they will take frozen foods(i.e. Mysis shrimp.) Enrichment of the food is also a good thing to utilize. Selcon as a soak and gut loading are the easiest. Hope this helps. You may want to email some of the national breeders through email to see if they have any advice as well.
Actually, if you go to seahorse.org and the Propagation and Rearing Forum, you will see few if any use the krieisel style any more. My system of using 4L jars with the rounding of the top creating the circular motion about as close as it gets nowadays. There are a myriad of methods used now, with some working for some and not others. Many are starting to adopt the tub version scaled down from Dan Underwood's systems.
It took me until the tenth try to be successful raising H. reidi fry and only about 30% got to four months. Successive batches have gotten to 60 to 65% now, with Dan Underwood getting 80 to 90% depending on the various species he raises.
If you are raising benthic fry species like southern erectus, then you usually can start right off with ongrown enriched bbs.
If you are raising pelagic fry like reidi or kuda, most times you need to start with enriched rotifers, and, if you have some, copepods appropriately sized.
Usually after the first two weeks for pelagic, I mix rots and enriched bbs and after they reach 4 weeks old, only the enriched bbs.
The best enrichment for rots and brine is Dan's Feed from seahorsesource.com.
It comes in powdered form and is a balanced food with a lot of extra's to it. It also will store a lot longer than the Selco/Selcon emulsions.
The Selco/Selcon emulsions are only enhancing the huffa content (fatty acid) whereas the Dans Feed does that plus protein and vitamins and even Beta Glucan if you want that version. Some pictures and description of my H. reidi fry raising