SEASONAL CARE Oxygen in the pond – winter Oxygen is readily soluble in cold water Oxygen in the pond – summer
Blanketweed produces oxygen during the day, but consumes it at night.
Less oxygen is available in the water as the temperature increases.
The fish are producing less waste and the lower temperatures inhibit bacterial activity
The koi are inactive at low temperatures and their oxygen requirement is minimal
More solid waste accumulates in the filter and this increases the demand for oxygen by the aerobic bacteria.
Note the decrease in percentage
saturation as the temperature increases. To compound this, the extra activity of the fish and increased amount of waste generated adds to the Biological Oxygen Demand (BOD) – the biological processes which collectively use up oxygen in the pond. So it’s important to maintain good hygiene by removing as much mulm, detritus and uneaten food as possible, thus reducing the BOD, whilst at the same time ensuring suitable oxygenation. Symptoms of depleted oxygen levels
include dyspnoea, or ‘piping’ (gasping) at the water’s surface – when fish are performing this behaviour they are trying to utilise the slightly higher oxygen concentrations in the very top layer of the water. Of course, we don’t want the fish to get into this state in the first place – hence the value of testing – but we need to employ a few simple principles, whether testing is carried out or not. One of these principles is to ensure that
Keeping up with any algal control
strategies which have been employed since the spring is vital
36 KOI CARP
the water in the pond is turned over through the filter (and any waterfalls etc) on a regular basis. Don’t be over the top though as too rapid a flow rate may impair the efficiency of the filter. It’s not necessary to actually aerate the
water to oxygenate it – it’s the turnover of water that’s important, exposing oxygen- depleted water to the atmosphere. Of course, aeration can be employed, and this can be extremely effective, as it draws water from the bottom of the pond to the surface. Contrary to popular belief, the bubbles
At higher temperatures, the koi are increasingly active and need more oxygen.
themselves dissolve a negligible amount of oxygen directly into the water.
every koi keeper’s dread We’ve previously seen that, for many
hobbyists, spring marks the onset of the dreaded ‘algae season’! The algae in question can be of two types – filamentous algae (or blanket weed) and unicellular algae (which cause green water). As temperatures continue to rise, and the
nutrient input into the pond increases, the situation can worsen considerably, so keeping on top of water changes and reducing levels of nutrient input (in other words, not overfeeding) will be necessary. Keeping up with any algal control
strategies which have been employed since the spring is vital. Algal control can be important for several reasons. Firstly, from an aesthetic point of view, it’s considered a bonus by many koi keepers to actually see their fish and green water can hinder this – often completely. Blanketweed can be a real problem for
pond keepers owning sturgeons and sterlets, as these are very prone to becoming entangled. This can often result in the death of the poor old fish. Finally, whilst algal growth may not
necessarily be a bad thing (and is, after all, natural in moderation), it can be a problem in excessive amounts. This is for two primary reasons; during the hours of daylight, very dense algal growth can lead
Pictures opposite and diagrams courtesy of The Interpet Manual of Koi Health
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