I've recently found out that using a magic eraser (just the plain one with no chemicals added) has worked really well at cleaning the corners of my aquarium. My trochus snails have been neglecting the more stuck on algae so I ended up having to do it manually. I normally use a metal algae scraper but it doesn't get really close to the edge and I didn't want to risk damaging the silicone with a razor blade. The sponge works well on the tough stuff and from what I can tell is not damaging the silicone. Just thought I would share!