The use of a sand filter media in a garden pond as a biological pond filter is not a good idea, although there are those fish keepers who still use one as a means to remove solid matter.
sand filter media are used extensively in fish hatcheries, sewage treatment applications and in swimming pools (particularly in warmer climates like South Africa, Australia and the warmer southern states of the USA).
Sand filters from a cost point of view are expensive to run and havent been designed to remove the nitrogenous waste matter (ammonia) that needs to be removed from any garden pond or fish pond.
They have instead been designed to remove large particles of waste, although they do perform nitrification of ammonia, to a lesser extent.
The major purpose of a biological pond filter in any fish pond or water garden is to remove ammonia, which can be highly toxic to pond inhabitants in high concentrations.
The biological process responsible for removing ammonia is known as the Nitrogen Cycle and is critically important to any aquatic pond system.
The secondary function of a pond filter, which many novice pond keepers actually believe is the real purpose of a pond filter is to mechanically remove pond debris such as leaves and other organic matter such as flocculated algae (dead algae that has been destroyed by a UV sterilizer and has clumped together).
This article will hopefully help to convince you that using a sand filter in your garden pond actually has more disadvantages than advantages. I will also recommend suitable alternatives to using a sand filter for biological pond filtration purposes.
Why Are sand filter media Bad For A Garden Pond?
Before I discuss my reasons why I believe that a sand filter has no place in a garden pond, I would quickly like to add that I am referring to a mechanical sand filter and not a fluidized sand filter, which has been designed for use as a biological filtration system for use in a pond environment.
As stated earlier in this article, sand filters are expensive to run on a continuous 24/7 basis. They also offer very little if any nitrification properties. The reasoning behind using a pond filter in the first place is to remove ammonia from your garden pond before it creates a toxic environment that is unsuitable for aquatic life, including pond fish, snails, frogs and toads etc to live in. Without the ability to perform the nitrification process (nitrogen cycle) which removes ammonia, it just does not make sense to me to use a sand filter as it doesnt perform this critically important function.
In a pond environment containing ammonia, it is the nitrifying bacteria, Nitrosomonas and Nitrobacter that are responsible for converting ammonia (toxic), firstly into nitrite (toxic) and then into nitrate (much less harmful). These microscopic beneficial bacteria live on the pond filter media, housed in the biological pond filter chamber. In order to ensure optimum ammonia conversion, certain criteria must be met: Firstly, oxygen needs to flow through the filter media as the conversion requires lots of oxygen; secondly a pond filter media with a high SSA (specific surface area) should be used to allow much larger colonies to form. The larger the biomass (size of colony) the quicker the ammonia will be broken down. Thirdly, turbulence which throws together water, oxygen and ammonia will significantly help to increase the rate at which ammonia can be broken down.
Some Discussion On Pressure Sand Filter
pressure sand filter consists of a pressure vessel-this could be either vertical or horizontal-fitted with a set of frontal pipe work and valves, graded silica quartz sand supported by layers of graded under bed consisting of pebbles and gravels, a top distributor to distribute the incoming water uniformly throughout the cross section of the filter, and an under drain system to collect filtered water.
Raw water flows down wards through the filter bed and as the suspended matter- which has usually been treated by addition of a coagulant like alum- is retained on the sand surface and between the sand grains immediately below the surface. There is steady rise in the loss of head as the filter process continues and the flow reduces once the pressure drop across the filter is excessive.
The filter is now taken out of service and cleaning of the filter is effected by flow reversal. To assist in cleaning the bed, the backwash operation is often preceded by air agitation through the under drain system. The process of air scouring agitates the sand with a scrubbing action, which loosens the intercepted particles. The filter is now ready to be put back into service.
Picture Low Flow PSF (FRP Vessel) and High flow custom Vessel (MS Vessel)
Advantages and Features
1. Efficient Turbidity and TSS Removal
2. Filter up to 20 30 Microns
3. FRP, CS, MSEP, SS Vessel available
4. ASME Pressure Vessel is also available
5. Standard and effective silica quartz sand media
6. Low Pressure drop across the vessel
7. Air scouring available for high flow pressure vessel
8. Automatic Valves are provided as per customer need
9. Manual, Semi Automatic and Automatic features are provided