Never switch off your pond pump for more than a few minutes if you keep fish.
A pump in a fish pond serves a very important reason. Of course, it circulates the water and it drives a fountain or a waterfall. Yes of course it adds character and movement to your system.
Its most important job with a pond pump is to provide life-giving oxygen to bacteria in the fish pond biofilter.
A pond pump works like your heart … the heart continuously replenishes your vital organs with freshly oxygenated blood. A pond pump in a pond does the same.
This is what’s happening in a pond
- Water absorbs oxygen at any interface between water and air and the more intimate this interface can be made then the better the rate of transfer of oxygen from air to water.
- Colder water can hold more oxygen than warmer water and is the reason why trout are difficult to keep in any garden fish pond.
- Windy days are better than still days for absorbing oxygen because the ruffled water surface and wind make mixing at surface regions more efficient … the surface absorbs the oxygen from the air then the wind movements mix the upper layers of oxygen-enriched water into the lower layers of the water body.
- Water has more oxygen in it during the day than it does at night especially if there are pond plants growing in the pond. Plans give off oxygen during daylight hours (photosynthesis) and absorb oxygen from the pond water at night.
A waterfall and a fountain are extremely useful in a pond because they increase the interface between water and air (small droplets have large areas) which allows for more air to be absorbed.
Now some of this dissolved oxygen is used by your fish to breathe and most people do realise this.
What people do not realise very well is that water when it enters the biofilter has a certain amount of oxygen in it ….. let’s say 100% for ease of understanding.
The bacteria in your biofilter are waiting for some food (nitrogen chemicals from fish waste) also dissolved in the pond water to reach them and they will also remove some of the oxygen in the water reducing the 100% to a lower value … maybe even zero. Let me explain in a simplified but essentially accurate way …….
In order to digest this incoming food each bacteria needs a small amount of oxygen. This oxygen combines with the nitrogen molecules and eventually becomes what we call nitrates. Initially the nitrogen chemical food source before it is converted by the biofilter bacteria is called Ammonia and its chemical formula is NH3.
Notice ammonia contains no O … for oxygen …. only N for nitrogen and H for hydrogen.
The biofilter bacteria, Aeromonas and Pseudomonas, convert the waste ammonia to nitrates. Notice what was initially NH3 has changed to a new chemical formula going by the general name of nitrates. The formula for nitrates is NO3. So what has happened?
The bacteria have removed the H from ammonia and exchanged it for 3 oxygen atoms. The H dropped from the ammonia molecule also combines with more O to form H2O … water.
It should be obvious from this very simple explanation that a considerable amount of oxygen is needed to allow the bacteria to do their work.
Consequently, the water leaving the biofilter does not have 100% oxygen but in fact much less. In very efficient biofilters like the modern filters from the UK company Aqua Evolution most of the oxygen is removed and has to be quickly replenished if the bacteria are not to die.
So now you know …. never switch off your pond pump for any length of time if you keep fish and certainly never during feeding.
Here are three very practical implications that you should take into serious consideration when you buy a pump …
- Will your retailer always ensure that you will have a pond pump if yours breaks down during the guarantee period?
- Two pumps are almost always better than one pond pump, very often cheaper too, and this means you always have a spare pump for an emergency.
- All biofilters benefit from adding extra air directly into the active biological area inside the biofilter. Without extra air over-designed static bed biofilters can in fact create anaerobic filter areas.
How To Convert Different Measurement Units
You will almost certainly at some time or another need to convert pond pump volumes or flow rates from one type of unit system to another. For example, gallons in the USA are not the same as in the UK. In fact, 1 imperial gallon is equal to 1.20 US gallons as you will see from the table below.
How To Use This Table
Look for the cell which contains the number 1. Then read across the row. For example, 1 cu Foot/min = 7.48 US galls per minute or 6.23 Imperials galls per minute or 28.32 liters per minute, and so forth.
This is particularly helpful in specifying pond pump and waterfall pumps
| Unit | US galls/min | Imp galls/min | Cu Feet/min | Liters/min | Cu.M/min | Lbs water/min |
| US gallons | 1 | 0.83 | 0.13 | 3.79 | 0.004 | 8.3 |
| Imp Gallons | 1.20 | 1 | 0.16 | 4.55 | 0.005 | 10.0 |
| Cu Feet | 7.48 | 6.23 | 1 | 28.32 | 0.028 | 62.4 |
| Liters | 0.26 | 0.22 | 0.04 | 1 | 0.001 | 2.2 |
| Cu.Metres | 264.20 | 220.00 | 35.32 | 1,000.00 | 1 | 2,202.7 |
