I know this is an older post. I have a fiberglass pool without tile and I get a scum ring by the waterline. I like the magic eraser, but I will pick up some actual pool & tile cleaner. I use the heavier duty magic eraser. They also make a bath one now that is supposed to be better for removing soap scum. I've tried both, but don't have a scientific comparison on which worked better. I was wondering what people's thought were on robots that clean above the waterline such as the Active 20. I would expect a hand cleaning would be required from time to time, but that a robot that gets above the waterline would be good for maintaining the cleanliness of the area and cut down on the work I have to do.