I have a pond approx 3/4 of an acre and about 10 ft deep. It started to get a lot of grass in it this year so I put a sump pump down in it and made a fountain head for it. It seems to be helping to clean the top 12 to 18 inches of the pond. I also put in some grass carp to help control the grass do I need to place the pump at the deepest part of the pond to get the best results?
Good move on adding the grass carp, better than using chemicals at least in my book. Just be careful not to over stock the grass carp. Use them to manage the weeds not eradicate the weeds. When the weeds are gone what will the grass carp eat? They could eat at the banks of the pond, cause corrosion or root up the bottom clouding up the pond.
You are started in the right direction by getting the water moving in the pond and yes pushing up from the deepest depth would be best. Don’t start running the pump full time from the deepest depth as there should be a start up procedure so we’re not pushing all the non oxygenated water and toxic gasses up and into where the fish are, just a little each day to help send the toxic gasses to atmosphere. Also check out Aerator startup.
I’m not too sure on the size of sump pump being used, how many gallons per hour it moves. But the goal is to turn the entire volume of water over once a day.
With a quick calculation on the pond size you have given and found approx. 1.9 million gallons of water in the pond, depending on what the slopes are and the shape of the pond. Moving water is more costly than moving air. Here’s an example of the PS30 bottom diffused aeration system, with the diffuser placed at the 10 depth. This aeration system can move 3,390 gallons of water per minute with air, turning over the entire pond volume twice a day so it could just be run 12 hours at night if you wish to. The compressor only a ¼ horse to pump the air required to turn over the complete volume of the pond.
Using a sump pump, for example a ¾ horse with 10 foot lift would provide 2700 gallons per hour of water movement. 
Adding the spray nozzle would choke the flow down some but even running at full bore for 24 hours would only provide 65,000 gallons of water movement using a ¾ horse sump pump.
Electricity is on the rise so by lowering the horse power to move water with air would be cheaper than moving water with water. If you want to see a display above the water surface use an aerator fountain. These are designed to move a lot of water and the added benefit of splashing back into the pond can add oxygen as well, depending on the brand some can aerate up to 30” deep.
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