Seahorse info

Hello my name is Matthew I have been in the roofing hobby for a while although I am only 13 I am highly educated and looking into seahorses I recently bought a 15 gallon aquarium from Petco it is a column tank 24 inches tall and probably around 18 wide perfect setup from what I've heard I know it's a little bit small but I have been able to keep up with some very difficult things to keep up with including very heavy bio loads all that I wanted was a pair of Tiger Tail seahorses and a mandarin goby so that would be a pretty cheap setup also wanted to stock it with macroalgae to help with biological filtration please let me know anything you have to say on this subject any posts will be appreciated please let me know how difficult it is to keep what kinds of people to look for common diseases and what the best thing to feed them is I am not willing to take the time to hatch live brine shrimp that is why I wanted larger seahorses than the Dwarfs thank you