Oxygen concentrations fall in warm weather... consider extra aeration using airstones or venturi devices and other diffusion devices

Oxygen quite readily dissolves passively diffusing from the atmosphere, but this limited amount is insufficient to satisfy the demands of koi and other oxygen-loving pond organisms such as beneficial bacteria and invertebrates in the filter.

Oxygen can often prove to be a limiting factor for fish and biofilters with the health and performance of both benefiting from additional aeration, especially during the warmer summer months.

• This can be achieved in a number of ways using water movement or the injection of air.
• Besides ensuring an adequate exchange of gases, aeration is also useful at helping to mix and circulate water within the pond, reducing the presence of dead-spots.
• Working in a similar fashion to an aquarium pump, a pond air pump is engineered to be able to pump larger volumes of air to greater depths.
• This is desirable, as to be effective, air must be delivered to the very bottom of a pond to provide the most efficient aeration and mixing.
• These are a cheaper alternative to the Hi-Blow, but will not serve as many air stones or no where near the depths of those reached by the Hi-blows.
• These diaphragm air pumps are silent running, and will work tirelessly for many years between diaphragm replacements.
• The air delivered by an air pump must be used efficiently by an air diffuser, as this will significantly affect its oxygenating performance.
• A venturi is an adapted piece of pipework which will draw air into a stream of water as it is pumped into a pond from a filter chamber.
  
  air pond pump water aeration oxygen-loving bottom diffuser koi Hi-blow diaphragm venturi "air dome" mixing depths click for full article