you can put hydrilla.sp(strong plant but still need a routine lighting ,not need CO2 ) or some waterlettuce(but this plant need a high lighting)
if you put plant on your tank you must know the risk
as we know average water turtle are really messy and there is a risk he will destroy it,but the advantage is water plant will be a veggie filter which absorbing amoniac,produce 02 and will increase the quality of your water tank
think about it dude