I sure do know about Czerny and his exercises, but I feel that every thing does not have to play at an ultra fast tempo, not until your hands can handle it better without being tense. I would recommend that you play at a slower pace, until your hands becomes more relaxed. The hands should never get tense in the first place while you play anything on the piano. What you can do, is stop playing, once you feel your hands tense up, just drop your arms to your side and shake your hands for a few seconds,and then lift your arms to the square and place your fingers upon the keys. Also, check how your wrists on how theyfeel while you play a piece. Are they too high or too low and being tense? Hope that will help you,
best wishes,
go