Why should I oxygenate my pond before a thunderstorm - especially when using PURE Bacteria?

Why could thunderstorms put my pond at risk?

Thunderstorms often follow long, hot, and dry spells—conditions that already reduce dissolved oxygen in pond water. Warm water holds less oxygen, and stagnant conditions allow waste to build up and increase oxygen demand.

When a storm arrives, the drop in atmospheric pressure slightly reduces water’s ability to hold oxygen (around 1% per 10 mbar drop). But more significantly, storms can cause pond turnover—a sudden mixing of deeper, oxygen-poor water with surface water. This can rapidly decrease oxygen levels at the surface, where your fish live.

What is pond turnover?

During warm periods, ponds often form layers:

• The surface layer (epilimnion) is warmer and oxygen-rich.
• The bottom layer (hypolimnion) is cooler and oxygen-poor due to accumulated organic matter and lack of circulation.

This layering is usually stable. However, storms—especially those with strong winds, rain, or pressure changes—can disturb the layers. This causes the cold, oxygen-poor water at the bottom to mix upward, reducing the available oxygen in the top layer and placing fish under stress.

What does PURE Bacteria have to do with it?

PURE Bacteria contains aerobic beneficial bacteria, which need oxygen to function. When added to a pond, these bacteria quickly activate and begin breaking down organic matter, a process that consumes oxygen.

If oxygen levels are already low due to weather conditions or pond turnover, this additional demand can further reduce the oxygen available for your fish.

Doesn’t rain help add oxygen?

It can—mild rain and surface agitation may introduce oxygen into the pond. However, the overall effect of a thunderstorm can still reduce oxygen because:

• Bottom layers of low-oxygen water mix to the surface.
• Bacteria and algae activity increases, consuming more oxygen.
• Organic debris may be stirred up and begin to decay, further reducing available oxygen.

How can I protect my pond and fish?

To maintain healthy oxygen levels and reduce fish stress:

• Keep aeration running at all times, especially before or during storms.
• Do not turn off air pumps, fountains, or waterfalls.
• Use PURE Bacteria only when oxygen levels are stable and adequate.
• Avoid overfeeding during hot or unsettled weather.
• If possible, monitor oxygen levels using a dissolved oxygen test kit or meter.

Bottom line:

Storms can cause sudden drops in oxygen—just when fish and bacteria need it most. Maintaining strong aeration and using PURE Bacteria helps maintain a healthy, stable environment for all pond life.