Contrary to what a lot of people think, brine shrimp to NOT take in liquids and filter out the food, but rather they capture appropriately sized particles that pass through their appendages, then passing the particles to their mouth using the appendages. They don't filter feed like say a clam would.
To get them to ingest liquids then, you need to emulsify them first, like Selco/Selcon have been already done.
Some people use egg yolk to emulsify liquids but I'm not sure just how effective egg yolk is as an emulsifier.
(Names of common emulsifiers include soy lecithin, mono- and diglycerides, egg yolks, polysorbates, and sorbitan monostearate.
A less efficient way is to wet the spirulina with Seachem Focus and then add the liquids and in this way some of the liquid will stay adhered to the powder for the brine to uptake.
The fish oils and Selco/Selcon's are not sufficiently high in DHA component for seahorses. They do have EPA.
The best enrichment for fatty acids with the highest DHA component is Algamac's 3050 powder.
I mix some of this with the spirulina powder I make brine shrimp food from.
Whatever you use, it needs to be blended in a blender for at least 2 minutes.
For ACCURATE information on anything to do with brine shrimp go to:
http://www.fao.org/docrep/003/W3732E/W3732E00.HTM
Scroll down to section 4.0, Artemia.