Be careful with putting lilies in the pond, they could get outta hand and trying to control them wouldn't be fun. Have you looked at the cover thread in the archives?
This one I'd consider stocking a bunch of RES, they would help with the mussel problem. What type of mussels are they?
If you have a large water inflow and outflow, that may be a large contributing factor in not being able to sustain a photoplankton bloom. If that's not the case, have you tested the water for alkalinity and pH? What type and how much fertilizer are you using?
