Put some into the coral gravel of a tank and leave them alone. They feed on the algae and reproduce and grow well, although the culture may have to be restarted from time to time. Baby guppies and mollies etc . Use new born fish and only place a few in the tank as fresh water fish die quickly in salt water. If you live on the coast, get a fine mesh plankton net to catch wild plankton.
Plankton is probably particularly important for brooding males.
Give size appropriate shrimp to seahorses. Seahorses are not usually very interested in them and only take the larger ones. There is a danger of Daphnia fouling the tank because the Daphnia die quickly in salt water. Tubifex, chironomid larvae etc . Basically ignored by seahorses.