Just like malkore- I have no idea y you would want to put sweet potatoe roots in your tank.
I don't know about the roots, but I have sweet potatoes growing around my house and from what I've seen don't left the potatoe part of the plant- were it stores it's energy/ food- get wet- don't put it in the water. Maybe a little wet but if it's damp all the time or wet/submersed it will start to rot/grow fungus.