Lack of Oxygen is the biggest risk your fish face during the summer months. Warmer water has a reduced ability to hold oxygen. Couple this with an increase in demand from your fish, and the fact that aquatic plants actually demand oxygen at night instead of producing it and this can result in serious problems.
How do you know when your pond is short of oxygen?
You may not know until too late when you look one morning after a hot, sticky night and some of your fish have gone belly up. If you lose fish overnight during a hot spell for no apparent reason, it is more than likely through lack of oxygen. Tell tale signs are that it will often be the larger fish that go as they demand more oxygen then smaller fish. Or alternatively that you just lose Golden Orfe or Sturgeon as they are the most oxygen demanding pond fish commonly available.
How to fix it
Aeration is the key to increasing vital oxygen levels and reducing harmful CO2. Garden ponds can be aerated in a number of ways. The simplest being circulating water with a pump – a Fountain Pump or Waterfall are best, though beware that turning these off at night often causes problems. You must leave fountains or waterfalls running 24/7 in hot weather.
The reason most people turn off fountains and waterfalls is generally to reduce noise at night. If this is the case consider a Pond Air Pump instead. Air Pumps such as the Evolution Aqua Air Pump range or Hozelock Air Pump models are designed specifically for pond use. These Air pumps are outdoor rated and ideal for adding the extra oxygen your fish require during the summer months. The major advantage is that they will efficiently aerate at a noise level that won’t be audible.
Air pumps provide aeration via Airstones which can also aid with pond filtration. Filter bacteria are aerobic and the more oxygen you provide them with the more efficiently they do their job. Dropping an air stone or two into your Pond Filter will more often than not allow the filter to cope with with more waste.