Not sure what they are made of but I will look when I go to the store. But I looked close at the plants and it is spot algae. Will a aquarium brush clean them or is their something I need to use?
I use a non scratch scourer on the glass of my tanks, so maybe something similar but if you think it may damage them then try an aquarium brush. I think you just need to try and find what works.
Thats what i use on my nano in the corners. As they are curved you cant get an algae scraper in to clean them and its gentle on the glass...no scratches.