If you have a lot of shallow water you will always have at least some grass problems. If you have 5 acres then you are probably about 26 carp shy have of having enough, especially in your case. Draining and starting over is the best way to take control of your pond. It is also the most expensive. Adding to the dam will reduce your water shed(runoff)and it sounds like you already need all the water you can get. If you do not want to inccur the expense of draining you should treat the pond. There are chemicals that will eliminate your grass. You will need to check to see what is legal in your state. I would add more carp and then fertilize as heavy as possible. Make sure you get carp that are 10-12 inches long so that they do not become a meal for existing fish. Get a water analysis done so that you know exactly how to fertilize. We have a shallow pond here in south georgia, about 4 acres. We had a lot of 2-4 foot water. It took us about 2 years to get a handle on our grass problem, as we have a long growing season. We did however get it under control. It has been a great pond.