There's this myth in the hobby not to use any soap or cleaners on aquarium and/or accessories. Now you can use white vinegar and a razor blade, but since it's off the tank and in the sink or the back yard, you can use a cleaner like CLR to easily remove calcium/lime scale - you just need to RINSE WELL.
Footnote: Back in the day when I had all plastic decor/plants, the'd go in the dishwaher with some bleach about once a month! I clean [empty] aquariums and sterlite bins I use to culture daphnia with Dawn dishwashing soap. Sometimes I might use Barkeeper's Friend and a scotchbrite pad - you just need to RINSE WELL.