Dear Cat Dancer:
Well, your 12-gallon nanocube is way too small to consider any of the larger species of seahorses such as Mustangs or Sunbursts (Hippocampus erectus). On the other hand, it is spacious enough to house a whole herd of dwarf seahorses (H. zosterae) and all of their offspring, but the nanocube would require extensive modifications in order to assure that the water flow was not too overpowering for the seahorses and that the filters did not suck up all of the newly hatched brine shrimp before the dwarfs had a chance to eat it.
The suggested stocking density for Zulu lulus or Cape seahorses (Hippocampus capensis) is one pair per 5 gallons, with a minimum tank size of 10 gallons. So your 12-gallon nanocube could house a pair of H. capensis seahorses if you are able to modify the circulation and add an aquarium chiller that can maintain the water temperature of the aquarium within their comfort range at all times. (H. capensis is a temperate or Coldwater seahorse and the optimum water temperature for Zulus is 68°F-72°F.)
Ocean Rider is the only aquaculture facility that works with these endangered seahorses, Cat Dancer, and I don’t believe they have any plans to make them available to the general public again in the foreseeable future. So it is likely to be very difficult for you to obtain any H. capensis at this time.
You may be better off considering the black Seapony (Hippocampus fuscus), which is another of the Shetland pony class of seahorses that could be considered for a modified 12-gallon nano tank. This species can be considered a tropical version of H. capensis, and it shares many of the admirable traits that make Cape seahorses desirable aquarium specimens. Hippocampus fuscus are excellent starter seahorses, produce benthic babies that are considered relatively easy to raise, and are the right size for smaller aquarium. Captive-bred-and-raised H. fuscus are available for hobbyists at this time, and do well at 72°F-75°F.
If you contact me off list ([email protected]), I would be happy to e-mail you complete species summaries on both H. capensis and H. fuscus so you can read more about their aquarium needs and requirements, Cat Dancer.
Best of luck finding just the right seahorses for your needs and interests!