by saying that it isn't "true aquatic" we mean that it isn't meant to be completely submerged in water....plants such as mondo grass, which isn't truly aquatic, work great in terrarium/vivarium type settings where the roots are in the water and the plant grows above the water line...it may only take a few days for it to start rotting or it could take a couple months - it all depends on how hardy it is....since it didn't sag at all i would have to say there is a 95% chance it isn't truly aquatic...it won't necessarily harm the fish, per se, leaving it in there for awhile, but eventually will most likely rot and deteriorate the water quality....try to find some water sprite or water wisteria - they will give you a similar look and are true aquatic