does not erase easily

These are more permanent than I would like. Doesn't erase fully when fresh. I left writing on my whiteboard for a few weeks, and had to use industrial cleaner to get the ink from these markers off. (note: a colleague was using an expo marker on the same occasion, and that erased fine after a few weeks) Maybe I'm doing something wrong. I don't have dedicated cleaner spray so maybe people are having luck with that. The color is very clear, not smudgy. Opaque. That's a plus.

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