Pond Boss Forums INTRO Questions & Observations pond turnover

scott69, a turnover and a DO crash are different things, and have different causes.

A cold rain could cause a "turnover" at any pool level in a non-aerated pond. A fast, sizeable amount of cold inflow into warm water (or warm into cold) causes the water to mix or "roll over" quickly and poisons the water and fish. In the summer, the colder bottom water becomes devoid of oxygen, anoxic, and poisonous from hydrogen sulfide and other toxins released from anaerobic bacteria after all oxygen is consumed around late Spring. The thermocline virtually stops the colder water from mixing in the upper warmer water column so the toxins can be released, mixed and/or diluted gradually or more oxygen can be dissolved.

In a DO crash from several cloudy days, the pond needs a fairly heavy planktonic algae bloom that is thriving (or heavy vegetation that needs LOTS of sunlight to live). When you get a few heavily cloudy days, the algae dies, then begins to decay, consuming large amounts of dissolved oxygen and possibly suffocating the fish.

Quality, well designed bottom diffused aeration will eliminate a turnover kill, and can help minimize a DO crash potential. For a DO crash due to a heavy bloom die off, or with a high load of biomass, high horsepower surface agitation is needed to really reduce a DO crash potential.

One other thing...Warmer waters in the summer can't hold nearly as much dissolved oxygen as cooler water can.