This link has good diagrams of the eyes and other physical characteristics used to ID tadpoles: http://www.pwrc.usgs.gov/tadpole/tutorial.htm
The big complicated key: http://www.pwrc.usgs.gov/tadpole/
And an easier to use reference for many of the tadpoles of eastern North America: http://fl.biology.usgs.gov/armi/Guid...dpoleGuide.pdf
Unless you physically remove the green frogs (which would be a temporary measure) or make the pond uninhabitable, you're unlikely to be able to remove them as they're pretty stubborn when they've found a spot they like. Gray's can lay a couple thousand of eggs so some of their offspring has a chance to make it past the gauntlet of pond predators, so overloading with tadpoles is the best bet.