As well as checking out the site for octo's, check out the best for seahorses.
http://www.seahorse.org
Seahorses, while occasionally surviving in reef type settings, have a very poor survivability in those settings.
For increased odds of survival, there are conditions that make it better, but many aren't interested in doing what it takes.
i.e.
Temperature 68° to 74°F max, to lessen the chances of bacterial infestation that they are prone to. (bacteria grow exponentially with each degree rise in temperature)
Species only tank, even to keeping the same species from the same breeding source preferably, as seahorses have grown up living with certain pathogens but many times succumb to pathogens other seahorses/pipefish carry as they haven't built up any immunity to them.
Buy TRUE captive bred tank raised seahorses that haven't encountered seawater. While the "net pen" or "cement container" raised ones come cheap initially, it's not cheap when the odds of loosing them are so much greater, or if you have to buy expensive medicines (some next to impossible to get now in Canada) to try and treat their afflictions.
Unfortunately, most seahorses labeled "tank raised" now come from places like Vietnam that use seawater in cement containers.