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.
Could the killjoys and permanently miserable go comment on a different sub? This is a supposed to be a wholesome place. I know Lemmy is filled with perpetually angry people but do you guys have to come here and complain about every detail?
I thought this was adorable and cute. Thanks for sharing OP!