did ya change the water, half each day? if not they were aspyhxiating due to oxygen deprivation. i have 50 wood frog tadpoles in two 10g tanks and only one died, because i accidentally crushed it under a rock. they will act stagnant and lackluster when the water is depleted of oxygen, but are instantly rejuvenated when new (unchlorinated) water is added. also you hafta start them in their own pond's water and gradually shift to other water! but if none of these worked, ok. they could spread rampant disease to the toads, though.