When it comes to seahorses, don't take ANY advice from them.
First of all, NO seahorse dwarf or standard feeds on phytoplankton of ANY species.
Dwarf seahorses will feed on live copepods and on brine shrimp nauplii, but most use the nauplii because it is extremely difficult to propagate sufficient copepods to sustain a dwarf culture. It makes a welcome addition to a feeding regime for them but the main food will be live brine ENRICHED artemia nauplii.
The only way it's good for dwarfs is if you are feeding the nauplii with it, but that is a very expensive way to go about it.
Sterilze the artemia cysts, or, decapp them, or buy decapped cysts, hatch out for a day, rinse, change water and grow out for another day until they develop their digestive tract, then rinse again and new water with enrichment in it and let them get gut loaded for 12 hours. Preferably then rinse again, new water and new enrichment and let go for another 12 hours and now the enrichment will not only be in the gut but it will be assimilated into the body of the naupii making them even more nutritious.
I prefer feeding 3 times daily and removing the previous artemia nauplii that have depleted their nutrient before adding the new enriched nauplii so the dwarfs can ONLY feed on enriched nauplii, not depleted nauplii.
I also recommend starting the hatching process ahead of time so you can get an idea of the work you will be involved with in keeping dwarfs.
Most people quickly tire of it and quit the hobby.
Hatcher/Enricher