the problem with fish in the seahorse tank is not necessarily one of agression. the faster moving much better swimming fish can outcompete the horses for food. horses take an eternity to eat. i turn off all the pumps in my tank, place their food in the old trydacna shell that serves as their feeding fish, and go upstairs and take my shower and get ready to go out. when i'm done, i turn the pumps back on (actually, i don't, i let alexa do it!!). they are very slow, deliberate feeders who knock more mysis out of the shell than they consume, which is a good thing because they then have to go hunt for it. but be careful about too many fish, particularly fast swimmers, in with the horses. in my tank, i have bangaii cardinals and pj cardinals, dartfish, mandarins, scooter blennies, and watchman gobys. all of these are very mellow and don't mess with the horses.