Biofilters need lots and lots of oxygen

This might sound strange but it is true as I will explain. However before I do I would like to discuss oxygen in terms of good and effective pond keeping.

One of the very best koi keepers in the world once said to me something I will never forget. Of course he was exaggerating a bit. Nigel said: "There should only be three things in a pond: water, fish and air ( ie oxygen)."

You may know that trout and salmon can only breed in running water such as streams or rivers. You will also know that these particular fish make hazardous journeys up to the very top parts of river systems where generally the water is shallow and full of gravel and the where water flows fast and riffley over the gravel. The water is also cooler.

The essential reason for these long perilous journeys to these headwaters are that the water is:

cool

pristine

clear

fast running

shallow

full of gravel

These conditions are absolutely essential to maintain the very high oxygen levels the fish and their eggs need to survive and produce offspring.

Air is absorbed by natural water-courses at the interface (the place where air and water meet - ie the surface). This air is then mixed by convection throughout the water mass. A tiny part of the oxygen in the air (air contains about 21% oxygen) is transferred into the water to be used by fish, plants and bacteria. On a calm summer's day in a lake the amount of oxygen in the lake would be lowered. The reasons are twofold: The interface between the air and the water is at a minimum because there is no surface movement.The higher the temperature of water the less oxygen (or air) the water can absorb and hold. On the other hand during a gale in winter the oxygen levels in a lake would be at their highest. The reason for this is the direct opposite to those above namely ........ The interface for air transfer into the water is at a maximum - waves rise, crash, break along the bank and continuously present a new air/water interface across which air can be absorbed by the water. And because the water is colder it can hold more oxygen. So what has this got to do with pond keeping? Notice I said oxygen in water is used by plants fish AND bacteria. Biofilters are absolutely essential in almost all ornamental garden garden ponds to purify the waste products excreted from the fish. In this way the fish are prevented from poisoning themselves to death. A biofilter can only work if it gets oxygen to feed its own bacteria 24 hours per day 7 days per week. Just like you and me biofilter bacteria die if they do not have air (oxygen) to breathe. This oxygen is contained in the water being pumped through the biofilter. Stop the pump, then you stop the water flow and after about 5 or 6 hours all the bacteria in the biofilter are DEAD. The bacteria survive a while because there is normally a bit of water left in the filter. Bacteria use this as their emergency oxygen supply. This is why we say after about 5/6 hours the bacteria die and not immediately the pump is stopped. Once the bacteria die and you continue feeding the fish toxic chemical build up in the pond water occurs. Do this when you have a highly stocked pond, the water is warm, possibly full of algae and you have a recipe for potential fish mortalities. The conclusion: Water must be pumped through a biofilter 24 hours per day, every day without fail except for very short maintenance periods. You cannot go to bed, shut off the pump until the next morning and expect your fish to like it.

Garden Fish Pond Keeping Articles To Explore

Select the correct pond & waterfall pump press green to listen

Best pondkeeping book on the web

copyright: 2002, this website and many others to do with water gardening and use of water in the home was created by Tony Roocroft who lives in Johannesburg South Africa