When buying seahorses there are choices to make with regards to sourcing.
First, there are still a few wildcaught seahorses being sold and they are the worst risk but usually the cheapest price.
Next comes TANK RAISED, or NET PEN RAISED, which means they are raised in pens in the ocean or more recently, in large cement tanks but in both cases, the ocean water is NOT treated and filtrated properly to take care of the pathogens present in that water. As such, they should be put through a deworming protocol (3 drugs 9 weeks total) like wildcaught should be to increase the chances of success in their keeping.
Unfortunately there are losses during the protocol.
The advantage that these have over wildcaught is that they usually have been trained to eat frozen foods.
These tank raised are the source of almost all the seahorses sold by LFS's in North America today and are cheaper than the preferred TRUE CAPTIVE BRED.
Now, the BEST source is to buy from breeders using artificial salt water like I.O. or from breeders who properly treat the ocean water they use, for the pathogens in it.
These seahorses (referred to as TRUE CAPTIVE BRED) are the most expensive, but have by far the better track record for survival. Even with these seahorses you don't guarantee their success, but you certainly improve the odds of success.
When buying from a store, or from an online company, ask who the breeder is and they should be able to give you that information.
If they don't, suspect the source to be tank raised, especially if they claim the seahorses to be true captive bred.
Breeders of true captive bred seahorses have no problems with any store they sell to, advising them of the breeding source.
It's very unfortunate that so many stores claim to be selling true captive bred when in fact they are selling tank raised seahorses.
Sometimes it is the store themselves responsible, and other times it can be their supplier giving them false information, but unfortunately it puts a bad light on the stores that truly do sell true captive bred seahorses, although there are not a lot of them.