Relativistic Hydrodynamics (RH) is a general approach that can be applied to any high-energy systems in extreme conditions, either in and out of equilibrium. Recently, it was seen that the gradient expansion of the RH can be valid up to a certain (critical) momentum, and this amount has a phenomenological consequence in the heavy-ion collisions. Moreover, the QCD phase diagram as a mother model has different parts that are separated by some critical lines, and looking to the RH near these critical lines and checking its validity regime are of great importance. In this work, we study the hydro of a special strongly interacting theory as well as the critical momentum. This model is the 1RCBH (1R-Charged Black Hole) that possesses a second-order phase transition near a critical point in the parameter space (T,\mu) of the boundary theory. This work is done in the ADS/CFT context and quasi-normal modes are used to determine the critical momentum. Details and discussions about this important topic will be given in my talk.