Thats 30 acre feet!!! Are you actually treating that much?? If you used Hydrothol you would probably use about 3-4 gallons per acre foot but would not recommend you using liquid if you are not licensed. Try some granular at 150# per acre foot. That may run you around $500-600 per acre foot retail. You may want to get a professional in there to do the job right. You can also use Aquathol K at 2.5 gallons per acre foot but I am not sure on the results. Both Aquathol K and Hydrothol 191 liquid or granular have Stargrass on their labels but have heard Hydrothol works better. Make sure its stargrass because if its not you will have an easier time treating the problem. If you have a photo post it here.
http://www.cerexagri.com/aquatic/hydrothol.asp