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How are the variances? Can we assume homoscedasticity? That is because KW also needs equal shapes, or at least to comparable level.
If you use Kruskal Wallis, I don't think Tukey is appropriate. A non parametric test should be used. I'd have suggested Wilcoxon, but as per Google and Stack Overflow, Dunn Test is the most standard post hoc after Kruskal. I actually haven't used this test myself, so can't say much.