i disagree that they are the hardest, i believe they are fairly easy. i have kept many species of horses successfully though. also it is nearly impossible to wean them onto frozen foods. and sometimes thats more of a pain that just doing brine.

many public aquariums cant even successfully wean them. as for sterile tanks that is correct, even the tiniest crab on a piece of live rock will make a snack of your horses. so no live rock live sand or tank mates for these little guys.