I've been looking into this one as well. Here's a few things to consider from the Florida EPA site:
"Turtle grass (Thalassia testudinum) is the best known, with its large, ribbon-like leaves that are 4-12 mm wide and 10-35 cm long. Two to five leaves per shoot grow from stout rhizomes that may be found as deep as 25 cm in the sediment."
You might want to consider this when setting up your DSB
in your fuge. It sounds like they need a lot of space for roots.
"Sea grasses are extremely efficient at capturing and utilizing nutrients, a major factor in their ability to maintain high productivity in relatively low nutrient environments (Zieman, 1982). They are apparently capable of absorbing nutrients through either their leaves or their roots. Zostera, a sea grass common in somewhat higher latitudes, can take up ammonia and phosphate from the sediments and transport the nutrients to the leaves, where they can be pumped into the surrounding water (McRoy and Barsdate, 1970). If turtle grass has the same capability, it should be of tremendous benefit to epiphytic algae on the sea grass blades, particularly in the nutrient-poor waters associated with coral reefs."
"pumped into the surrounding water ... where they can benefit algae" doesn't sound like what we're after. If this proves to be true, you might want to think a little more about macro's ... even though I have heard several sources (including yourself) talk about how the macro's can suddenly break down. This article does say "If
the turtle grass has the same capability", so this may not be the case.
I'm going to keep looking into this one. Let me know if you find anything.