Assuming you want a pair of seahorses and you want to keep costs down, then I would suggest a 20 gallon high tank for a pair of H. fuscus. You'll need filtration and oxygenation, so I also recommend a protein skimmer. Mysis shrimp are essential to seahorse keeping nowadays. Basic lighting should be fine. A small sandbed is also nice, but you may not need one, I would recommend one because you can also add Caulerpa macroalgae and Nassarius snails. The Caulerpa provides hitching posts, and also sucks up lots of nutrients that the seahorses excrete (I like C. prolifera personally). The Nassarius snails will eat leftover tidbits of mysis shrimp that the seahorses will most likely spew out.
