You can do water changes to keep the tank clean. I just got a lot of advice on my new tadpoles..
"Hi.
Tadpoles will stay tadpoles in cold water or start to metamorph in 76 or above water, either way you have a couple months before theyre froglets. they eat
Rinsed green pond algae
Duckweed
Elodea/Anachris
*Algae Wafers
*Goldfish & Spirulina flakes
*Frozen mixed greens, they can be fed just the last 3 and be fine...
10 gal. 3/4 full is fine for a few tadpoles. Froglets do good in 1" water w/ floats or 20 % land area.. use bottled spring water or well aged dechlorinated tap water only - and filter or better yet change often w/ tadpoles "
That's what I was told for mine. I hope this helps you out!