Well mine are parvocalanus and tisbe. Just because I have those in large numbers. Also I'm using the san francisco baby brine which are smaller.
I have read many just use baby brine shrimp but I've also read about high mortality rates.
I haven't purchased any books specific to seahorses but do have a couple breeding books.
I put in the copepods because I have them and they are superior nutrition. That also hold their nutrition if not eaten right away better than baby brine.
The other reason which I don't know if true or not. Someone else dissected their dead babies and found compacted brine shrimp exoskeletons in their digestive tract and postulated that brine over 3 hours oldish had hardened shells that contributed to the mortality. This same person believed after 3 days their digestive tract was then able to better handle the brine.
Things I know. My first batch I used brine the next day the babies were all dead. Not sure why but I suspect it was an ammonia spike or oxygen drop from the green water.
2nd batch I used a lot of parvocalanus because I only had a few brine hatch that day. Babies all made it for quite a while healthy and that batch is at about 50% mortality but mostly due to gas bubble disease and a rust getting in their water / water change incident.
3rd batch I used a lot of tisbe and brine lost them overnight. Again I believe due to ammonia and oxygen but MAYBE the too many tisbe adults.
4th batch happened 3/27 and I used a lot of parvo and too much brine. They were born during the day went through the overflow (most) had hours that they didn't have much to eat. Fished them out early evening. Too much brine (there were still tons of brine this morning), some t-iso and parvo. Only day 2 but so far only lost 2 which I think is awesome given their beginning.
I think you could easily raise some seahorses. You have to remember that nice picture in the beginning is my 'grow out' tank, I haven't even used that yet. Right now it is full of nannocloropsis and tisbe copepods.
When they are first born I put them in a 1.5 gallon plastic bin so that I can concentrate the food and make water changes easier. I use prime also. unheated room temp. I have added an air stone to help reduce the chance of gas bubble.
Then so far the next stage is a 7 gallon bin (dish bin for restaurants). Unheated room temp.
Now they are in the divided 20 gallon which I think they will be able to stay there for a while. I have it divided because was for another project but this allows the heater to be away from the babies. and I can concentrate the food in 10 gallons but have 20 gallons for stability. I also have more chaeto on the heater side to process waste. I'll be stocking it with tisbe copepods this weekend as well.
So when I say easy, I don't mean cheap
I doubt I'll ever make much money though I'm getting more efficient. I spend about 2 hours a day during the week and more on the weekend but that is for all my tanks, copepods, microalgae and such.