When I did my local bay tank, I had several patches of our local sea grasses. They were doing extemely well, growing and spreading, until my crabs got larger and dug them all up while burrowing. They were in about 3 in. of silty,sandy, substrate. I have 260 watts of light and left them on longer than normal for the grass. I'm about to move the crabs to a 75g I'm setting up to see if I can get the grass to grow back. Let me know how your grass goes.