Can I have a spider plant in my aquarium or would it rot/ruin the water quality? My mom has lots of spider plants, they multiple so easily and she just keeps them in water so when she asked if I wanted some of her extras I thought it would be cool to have them in an aquarium if that was possible.

I think it would be alright if it was only the roots in the water. I think the leaves would probably rot underwater at some point.

Yeah, that's generally the case with non-aquatic plants found for sale in the aquatic section at pet stores. The roots can be submerged and they can live and thrive like that, but the leaves cannot be submerged, so they're not fully aquatic.