The river frog (Lithobates heckscheri)
Tadpole pictured below


Breeding:
Breeding takes place between April and August with males calling from the edge of ponds and swamps from April to July. The call has been described as "a deep, low-pitched, rolling snore".

Eggs:
The eggs are laid in a floating layer among emergent vegetation, a clutch numbering several thousand eggs which hatch after about three days.

Tadpoles:
The tadpoles are at first a dark color but become much paler over time with a dark edge to the tail fin. They congregate in the shallows in the daytime, sometimes in dense swarms, but move into deep water at night. They feed on both animal and vegetable matter. They remain as tadpoles for a long period, overwintering once or twice, and reaching a snout-to-vent length of 97 millimetres (3.8 in) or more.

Metamorphosis:
After metamorphosis, the newly-emerged juveniles are 30 to 52 millimetres (1.2 to 2.0 in) long and move away from the margins of the water. The large number of juveniles compared to the relatively small number of adults indicates a high mortality rate for newly emerged young.

Sounds like you should someone incorporate a set up of a land hill into the tadpole tank so they may sit in shallow or deep waters and leave the water as they are ready. If this is indeed the tadpoles you have. Does the picture resemble the tadpoles?


-BrittsBugs
Reptile & Amphibian Enthusiast
Insect Breeder
Former Rat Breeder
Pets: 6 AUS WTF's, 1 Hon Milk, 1 SM Corn, 1 BP, 5 H.Crabs, 1 C.Gecko, 4 RB Newts, 6 Betas, 5 MH Roaches, 1 L.Gecko, 1 W.Hognose, & so much more