Hello and welcome to FF ! High levels of ammonia are indicative of a not cycled tank. Did you set-up the aquarium recently? Are those snails moving around/alive or closed up in shells? If so, could be dead and adding more ammonia to water. There is not much you can do for Ammonia burns other that moving the surviving tadpole to a cycled tank.

If tank is new set-up; do you have another older tank with filter material you could move into this tank? Need to start doing small 10% water changes couple times a day to bring that ammonia level down until aquarium cycles. Stop using Prime to try to reduce ammonia and nitrates; it interferes with the natural denitrification cycle. There are products in market that will accelerate cycling; try and get a bottle of Seachem Stability and follow the bottle label directions.

Also, adding 1 tablespoon of aquarium or kosher salt per 5 gal. of water to tank will reduce the toxic effect of ammonia.