That’s most unfortunate that two of your Hippocampus erectus also succumbed as a result of a power outage.
But, as we have been discussing, Hippocampus erectus can adapt to a very wide range of water temperature as long as the temperature changes are gradual enough. So if the other ponies are eating and looking fine despite the dramatic drop in water temperature, then I suspect they will be okay as long as you do not raise the water temperature too quickly. Be sure to take your time when raising the aquarium temperature.
One other thing to beware of is a spike in the ammonia or nitrite levels in the aquarium. It sounds like the power outage wiped out all of the fish in the tank except for some of the ponies, and if there have been any dead snails or other invertebrates whose loss may have gone undetected, that could cause your water quality to deteriorate. The sudden change in water temperature may also have had an adverse effect on the beneficial nitrifying bacteria that provide biological filtration, so be sure to keep a close eye on your water quality parameters.
Pete Giwojna, Ocean Rider Tech Support