Having trouble progressing with bicep curls

I've been on ICF 5X5 for about a month now, and while my squat, bench, deadlift and other lifts have been progressing nicely, my curls haven't been.

I've been using dumbbells because my right arm in general is a lot stronger than my left due to baseball and it being my dominant arm and I wanted them to balance out.

I started off with 20 lb dumbbells and now am on 22.5 lb dumbbells. I can curl 25's with my right arm but not with my left. Does anyone have advice on how to increase the weight or is this normal? Thanks for any help.