No way a Stream would work, having kept seahorses, I have watched a starfish eat one alive tail first. You have to be pretty slow for that to happen. I think a closed loop is the only safe way to accomplish what you want to do. billsreef is a bit of an expert on seagrass and I would highly recommend sending him a PM. My main suggestion- don't do seahorses, far more work than they are worth, I like the seagrass idea but their are so many cool fish that don't need 4-6 feedings a day and live more than a few years, ehh, don't get me started, far more work than they are worth and I get me fill of them at zoos and public aquaria.