I would say a lb or so for 5 gallons but maybe just taste test the salt water and go from there. Don't think you would need the dish soap, just watering with salt water should be sufficient
salt water did not kill it.
Literally pay a group of high schoolers to scoop them up and take them away. will need to happen quarterly because you know they will regrow. But eventually you'll get them all..
its around 25 acres. shoveling it up might be only way but it would take forever.