I think "painful to the eyes" is being just a little dramatic. Between page turns black flash (refresh) is to reduce ghosting of faint image from prior text showing on new page.
With you kobo mini turned on, touch center bottom of screen. Next touch 3 line icon at top right of screen. Next touch "settings" box in drop down menu box. Now touch "Reading Settings". Bottom 1/2 of first reading setting page is for Page Refresh Settings. Because your reader is refreshing after 1 page Touch box that says "1 Pages" than select "6 pages" from drop down menu. Your reader should now refresh only after 6 page turns.
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