It's not a good idea. Sea horses are very slow moving. They should be provided with something that they can hold on to an ideally a light water flow would bring the food to them. They don't usually do well if they have to compete for food with faster swimming fish.

good answer: sea horses can be kept in an established reef tank that generates its own "wildlife" in the live rock so they can forage for food as in the wild, since they normally eat live things they are always on the hunt, this is the same problem with the mandarinfish.

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As stated above with the mandarin goby it is recommended the tank be atleast 6 months established. Also as stated above light flow tanks are ideal as they are not very profecient swimmers and can not easily catch food. I would not introduce many types of fish with the horses as they are vulnerable. Gorgonia or other branchy saltwater decorations are needed for the horses to anchor themselves to to sleep and rest.

( buy de way my answer is bs )