Seahorses are suposed to be in species only tanks, or with pipefish I believe. They are very hard to take care of, and are hard to feed, I think they have to have newly hatched brine. And yes, go with the biggest tank you can afford, I learned the hard way! And I really wouldnt recomend seahorses. People here give a lot of help if you have questions about setting up your tank, so search some of the former posts and stuff and you will get alot of helpful info.