One thing to consider re: glass top or not --- will there be any sort of power head in the tank? Anything in the tank at all that will be plugged in? And if so, do you have cats? Dogs? Clummsy people that live with you? Despite all the beautiful branching rock and macro algae in a seahorse tank, most seahorses will hitch, from time to time, on the cords that power things that are inside their tank. This isn't a problem, per say, unless they are still hanging on when that cord is yanked by someone outside of the aquarium.... I have seen and read about horses that have held onto something only to be lifted from the water. Just make sure that all cords are well secured.