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my sister brought home a toad and wants to keep it in the same tank, is this okay or not?

No, the turtle will eat that toad. Plus, the toad might hurt your turtle, poison it or your turtle might choke on it. Also do not introduce wild-caught animals to your turtle.

Toads secrete poison from their glands (people think they are warts) when in danger. That may poison your turtle. You should build him a toad home in your garden if you have one. Just google it and you can learn how to make one. Toads also need a lot of dry land so a turtle habitat would not be suitable for a toad.