With seahorses...the current strength is what matters...too strong of current will carry the food away before they eat...and too strong will also stress them to the point of not eating=death.
Seahorses are an extremely delicate and time consuming specimen...I hope you have done thorough research into their habitat and care prior to attempting to keep them...they are enjoyable, but difficult to keep...and any bad water chemistry will stress them to death.
Good luck.