Pregnancy Chalkboard Pictures - Question?

Kristen • Hubby & I have been together 10 years, married 11/8/14. Angel Baby - 10/22/15. Rainbow Baby Girl, Maggie, born 10-18-16!
I bought a chalkboard for week by week pictures. The original chalkboard must have had some sort of coating on it because the paint from the pens would just bead up and never dry. So my husband and I painted over it with chalkboard paint. We used it last night and when we go to clean the board off the paint doesn't totally wipe off, we had to use a magic eraser and even then you could still see the old writing. Anyone else using a chalkboard for weekly pictures and having this problem? What's your secret? Thanks!
See the old writing?
These are the markers we're using, it's the second kind we've tried.

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