The lecture deals with theoretical and experimental study of flow pattern dynamics and its manifestation on liquid surface in flat bottomed and four baffled cylindrical mixing vessel stirred by down pumping six pitched blade turbine. Mixing vessel with inner diameter T= 0.29 m was filled with water to the height H=T. Diameter of impeller D was T/3, and impeller bottom-of clearance C=T. Width of baffles was b=0.1 T and impeller speed was set to 6.67 s-1 (400 rpm). Based on flow visualisation in middle vertical plane passing just front of opposite baffles, quasi periodical behaviour of macro-flow was detected and investigated. It was found, that responding macro-flow pattern can be divided to lower and upper part, with lower part express periodical behaviour of generating, growing and subsequently disintegrating of main circulation loop while upper part is characteristic by presence of so-called flow macro formation which are separated from main circulation loop and moving to liquid surface where some of them caused surface macro-swelling. Visualisation in horizontal plane passing through the vessel at 3/4 H shoved that mentioned flow macro formations are present just at the baffles with practically equal frequency for each baffle. And anyway so liquid surface macro-swelling. Furthermore was found, that while one cycle of main circulation loop, approx. 2-4 flow macro formation are separated within one quadrant of vessel. Described flow-pattern behaviour is supposed to be manifestation of well-known low frequency phenomena of flow macro-instability in mixing vessel.