I would personally avoid anything that stopped all plants from growing. The thought of that literally frightens me. I love the plan of using grass carp and they'll help but won't probably keep up next year yet will provide increasing control as their standing weight increases. I'd pay attention to the size and quantity they are able to control the naiad. This is the standing weight that can control it. Ideally, you need a ladder system that keep them at that standing weight within the context of natural mortality. Stocking at the ladder would then be the method of control. Transitioning to the ladder will be an exercise that you can begin now. When you reach control, you will be able to estimate a final ladder system going forward.
I'm different than most but I would not use chemicals to control this problem. When the growth reaches unacceptable levels, I would harvest the naiad using a rake I could pull with a tractor or 4 wheeler. I might transport it and its nutrients to spread and decay on a deer feed plot. I would harvest what the carp couldn't keep up with while leaving cover for my YOY and food for the carp. The amount of nutrients you remove should probably be equal to (the nutrients bound in annual feed) - (nutrients flowing out with water at the outlet annually).
If you try to control this problem with chemicals, it will have cascading effects that go well beyond controlling the naiad.
Is bushy pondweed something the Moz TP won't eat? I guess I am asking because I don't know the answer but without knowing I might think they would eat the southern naiad if nothing else were available for them to eat. TP can attain noteworthy standing weights so if they were successful at doing so why would southern naiad be so uncontrolled when TP are present unless perhaps they just won't eat it or possibly an alternative food is diverting them from eating it?
Does anyone out there control Southern Naiad with TP? Are TP an organism that can control it or must it be marked from the list?
There is an interesting discussion here:https://texasfishingforum.com/forums/ubbthreads.php/topics/8981219/Stocking_Tilapia_or_Carp
The thread referenced above said it was important that carp be present in spring when shoots are first developing. Once the naiad has grown and branched a lot ... a small number can't keep up. The control they provide should be much better next year and may be sufficient depending on how vigorously it grows. The carp you have now can eat 3/4 ton of vegetation a month!