First of all.... you shouldn't be feeding frozen brine shrimp. Your seahorses will slowly starve. You need to get frozen mysis shrimp, preferably PE Mysis or Hikari mysis. Thaw the food out (one cube per pair of seahorses) and feed them by putting the food in a feeding dish. The mysis will stay in the dish instead of blowing around the tank. This allows you to see how much each seahorse is eating. On average, a pair of seahorses can eat one cube of frozen mysis twice a day.
Hope that helps.
Tom