Here's my reccomendation, get plastic plants. THis way you don't have to worry about lighting and that kind of stuff because you have to remember that there are no salt water plants, it's just algae and algae need strong lighting to flow. If you get more lighting you can grow these 'algae' looking plants but that means you will get algae on your glass which means you need a better clean up crew plus loads of money for the lights.
If you get plastic plants you can do numerous cool things, like turn your sehaorse PURPLE, which would be mildly entertaining. Seahorses change color to their surrounding and if you get a plant that he likes and can hide and is very stable he will change colors. It's very cool...
Types of plastic platns... Long ones but thin. There are these fake plants that are eight inches high and kind of do a spiral all the way up. PERFECT for seahorses. BUt anything liked that will do fine. If you can get one that forms a sort of sphere shape, like i describe, it will be better for your future pony.
Shaving brush, not such a good thing... they can hide in them but have difficulty hiding.
JennyL, do you have a guard on your heater??? If not your seahorse is probably burning itself... think about it... if your seahorse keeps doing this i reccommend you get this heater behind rock work and away from the seahorse or get a guard...