The tank would need to be cooler, 72-74 degrees. Seahorses do not need a lower flow. They do need clean water, change about 25% weekly. Are the clowns hosting something that they will defend? Do you have corals, other than softies, that may sting? Have the clowns mated? They can be defensive when they do. What species of clowns do you have? Ocellaris or A. Percula would be the calmest, the maroons are some of the meanest. Were the clowns captive bred or wild caught. The seahorses are mostly captive bred and have not been exposed to things that wild fish will carry. They are susceptible to many diseases and are not easily treatable. Do you have macro algae or Gorgonians that they can hitch to? The seahorses are not great swimmers and they need something to hitch to. If I were going to do something like this, I would design the tank towards the seahorses needs and the clowns could adjust. Seahorses do eat mysis and will do better if they have access to some live foods, amphipods, brine shrimp… The seahorses require better care than a clownfish and you should do a little bit of research before putting them in with the clownfish.