In Ep1 Jack and all of the others have white belts, but then in Ep4 they all have yellow belts, then in Series 1 Ep9 Jack and Kim have black belts. The only one throughout the series who gets a higher ranking belt is Eddie in Series 2 Ep14 - from Yellow to Orange. But somewhere around the second season they talk about Jack as a second degree black belt, but no information when he got it is revealed either.