I don’t know much about 3d printer filaments, but wouldn’t that increase the plastic pollution of the water?
There is a special coating that you put on decorations not meant for aquariums that will prevent any chemicals from leaking into the water.
Plastic is pretty stable. Since this is an aquarium it isn’t get direct sunlight at a rate to make the plastic degrade to the point of polluting the water.
Also, since it’s an aquarium, the are already many kinds of plastics involved. The pumps, tubing, filters, and so on all contain plastic that would have a heater likelihood of degrade sure to mechanical action.