Page 5...Lava Rock Filter

NATURAL FILTER MEDIA
PEA GRAVEL	LARGER GRAVEL	LAVA ROCK	SAND	DIATOMACEOUS EARTH

SYNTHETIC FILTER MEDIA
BIO-BALLS	OPEN CELLED FOAM RUBBER	STRAINERS

FILTER MATS

SPIRALFLO

SIPORAX

BRUSHES

CONSTRUCTING OUR FILTER

~ FILTRATION 101 ~

THE THREE BASIC TYPES OF FILTRATION

CHEMICAL

Chemical filtration is the removal of algae, ammonia and phosphates, by the addition of other chemicals. This method works well in small reflective ponds where there are no fish or plants. We do not recommend the use of chemicals in a typical back yard pond. The only two exceptions would be...1. If it is a medication for your fish or, 2. If you have a high capacity filter that has been drained for cleaning, you can add a small amount of de-chlorinator in the filter before filling it up with city water.

MECHANICAL

Mechanical filtration is the physical removal of particles from the water by using one or more different types of materials. Polyester filters are among the most popular, they are usually a two stage type pad, each side having a different density. The coarse layer removes large particals such as leaves, grass and un-eaten fish foods. The finer side removes smaller particals such as dirt and algae blooms. Foam pads are also used but seem to clog up easier. Mechanical filters work well as a pre-filter but not recommended to be used as the primary filtration system. Do not use standard heating or air conditioning pads...they are usually made of fiberglass, which can break loose and harm your fish.

BIOLOGICAL

The biological filter uses two species of bacteria which feed on poisonous ammonia and nitrites, which is caused from fish waste, uneaten food and decomposing plants and leaves. The biological filter converts them to a less toxic nitrate, which is then used as a nitrogen source by plants. This continuous process is called the "nitrogen cycle".
The key to a properly designed biological filter is the media bed, which provides a place for the bacteria to live and grow. This type of filter requires a continuously operating pump in order to keep the good bacteria alive, which without water, can die within six hours.
There are as many different types of material that can be used as there are people using them. Below, you will find a list of the choices that we are familiar with. Each of these have their pros and cons, as we have learned through experience. A filter just isn't a filter if it doesn't have the right filter material. Fancy space-age bio-balls, lava rock, foam rubber, even old hair rollers have been tried and tested in the quest for clean water.
Filter material does two things. It removes particals from the water (machanical filtration), including fish waste, algae, dirt, and other debris. It also plays a role in removing harmful chemicals such as ammonia and nitrites from the water (biological filtration) by providing a surface for bacteria to live and grow. Filter material may work well for machanical and biological filtration, or it may only be suitable for one kind, but not the other. It's important to know what you want your filter to do for you.
It's also important to remember that all kinds of materials have their limitations. One is that water follows the path of least resistance. In other words, water will always try to go around the filter material rather than through it. Your filter media has to fit into the chamber, so that the water doesn't compleatly bypass it. Do not leave large gaps between the filter material and the sides of the chamber. Placing loose media in nylon bags may make it easier to remove for cleaning, however we don't recommend this because it makes it almost impossible to get a good fit around the edges.
Another limitation to all filter material is the effect of channeling. This occurs when sediment falls out of the water and attaches to the filter material, creating ruts and grooves that restrict and direct the flow of water. Bacteria usually will not survive where sediment build-up has occurred on the filter medium. Some kinds of filter material are more prone to channeling than are others.
Ideally, pond water should flow evenly over and through the filter medium. Even distribution makes machanical and biological filtration much more efficient. Particles are removed more completely. Bacteria has a better chance to colonize more of the filter medium.
Many filtering systems use two or more kinds of materials. For example, filter mats are used for mechanical filtration and lava rock for biological filtration. This makes it more convenient to maintain the filter and easier to position the filter in the overall pond scheme.
Filter materials fall into two general categories - natural and synthetic. Both serve useful purposes in filtering pond water so that it is clean and clear.

NATURAL FILTER MEDIA

Pea Gravel
Small gravel that's about the size and shape of peas, thus its name. It's very cheap and has a fair amount of surface area for beneficial bacteria to populate. However, it tends to be heavy and clogs easily with fish waste and debris. When this happens it tends to channel, limiting the amount of oxygen that reaches the bacteria. Pea gravel is also fairly difficult to clean. Overall, its use for biological filtration is adequate, while its use for mechanical filtration is below par.

Larger Gravel
Similar to pea gravel only larger in size.....it's usually sold in home improvement centers as landscaping materials. Because it's larger, it has less surface area. On the plus side, it doesn't clog up as easily as pea gravel, and it is slightly (but only slightly) easier to clean. Its value for both biological and mechanical filtration is adequate. Like pea gravel, it is usually inexpensive. Be careful if you use limestone gravel: it can alter the pH, leading to problems in water quality and potential illness or desease in your koi or goldfish.

Lava Rock
This was our choice....lava rock is fairly lightweight, very porous and has lots of crevasses, giving it excellent surface area for bacteria to colonize. Because of its many nooks and crannies, it does have a tendency to clog and channel somewhat faster than some of the other synthetic medias. It's ease in cleaning, more than compensates for this. It's also, fairly cheap, and it's much lighter than pea gravel or larger gravel. Bare in mind, when choosing your filter housing, even lava rock, when it's wet, still needs a strong container. A milk crate filled with wet lava rock can weigh up to 45 pounds. For both mechanical and biological filtration, lava rock is an excellent choice because of its cost and its ease of maintenance. Lava rock as a filter material is underrated and overlooked.

Sand
Builder's sand, beach sand or silica (pool) sand. Some filter systems use one of these types of sand to filter particles out of the water. Special sand filters usually use silica sand and are common in the pool industry. Sand is generally never used for biological filtration. It is inexpensive and highly effective in removing debris from pond water, however, it needs frequent cleaning.

Diatomaceous Earth
Similar to sand, only finer. Particles of diatomaceous earth are spined, not round like sand. The particles interlock, allowing water to pass through small holes where debris is lodged. Like sand, it is excellent for mechanical filtration, but of no benefit for biological filtration. Very effective in removing blue-green algae from pond water, diatomaceous earth generally costs about the same as silica sand. Often special filters are constructed specifically for diatomaceous earth.

SYNTHETIC FILTER MEDIA

Other filter media are man-made. At times, their cost may be rather expensive. Here are some examples.

Bio-Balls
Plastic open balls usually made of polyethylene. Normally bio-balls do not clog or channel. Their surface area is usually good, depending upon the size of the ball and the way it is configured. Bio-balls can have negative buoyancy (sinking) or positive buoyancy (floating) based on the material used in construction. Be sure that the bio-balls you choose, have a negative buoyancy. They are very good for biological filtration, but have minimal value for mechanical filtration. Bio-balls are typically used in trickle dry filters.

Open Celled Foam Rubber
The common foam rubber mat often associated with filter devices. It comes in a wide variety of shapes and sizes. Foam rubber filter mats have excellent surface area when they are clean, but they tend to clog very quickly and require frequent cleaning. Foam rubber is used for both mechanical and biological filtration and is especially common as a pre-filter for pumps. It is inexpensive and readily available. Some forms of foam rubber expand when they are wet, reducing the likelihood that water will simply slip around the filter rather than passing through it.

Plastic or Metal Strainer
Often found on the suction side of the pump. The plastic or metal strainer or screen acts as a mechanical filter, removing larager particles and debris, such as, leaves and grass. Often it requires frequent cleaning. Those with larger openings need less cleaning, but allow more debris to pass through to the pump. Plastic or metal strainers and screens have minimal value in biological filtration, although some beneficial bacteria will grow on them.

Filter Mat
Usually made of polyester. Mats are available in a multitude of sizes and are usually inexpensive. They have good surface area for bacteria to colonize, and are good mechanical filters to remove debris from the water. They are rated by their density from fine to coarse. Coarser filter material is less prone to channeling and generally needs to be cleaned less frequently. Although they are easy to find, inexpensive, and useful for pond filtration, polyester filters present their own set of problems, though. Water easily passes around a poorly fitted filter mat. Here are some tips on how to force water through the material. First, cut the mat larger than the opening where it belongs. Then, tightly pack the mat against the edges so that water must go through the filter mat instead of around it. Another solution is to make a frame for the mat so that the frame fits tightly against the edges of the chamber. Yet another method is to wrap the mat around a perforated, delivery pipe so that the water radiates out through the mat. Some pond owners use furnace filters, believing them to be a cheap and ready replacement for polyester mats.....they are not. Furnace filters often contain fiberglass, which can dislodge from the filter and float through the water, injuring pond fish. Make sure the mat you use is fish-safe.

Spiralflo
Either polyethylene or PVC ribbon. Thin and narrow, the ribbon has negative buoyancy and provides good surface area without clogging. Spiralflo is used primarily for biological filtration. Although it is more expensive than some other filter media, it is very easy to clean and is very long-lasting. Depending upon the configuration of the filtering device, it may have to be contained in a bag. Make sure the water passes through the Spiralflo, not around it. It has higher surface area per cubic foot when packed more tightly in the filter.

Siporax
Synthetic product similar to lava rock, made of sintered porous glass. Its small porous cylinders provide a great deal of surface area per cubic foot for beneficial bacteria to grow and populate. More expensive, Siporax is used primarily for biological filtration. Like lava rock, it's lightweight, and may have a tendency to clog and channel.

Brushes
Round, plastic devices. Brushes are typically used to filter out solid debris from pond water. They are also useful for biological filtration. Brushes are cheap and come in a wide array of sizes. They are easy to clean and generally long-lasting.
Other man-made products that pond owners use in their filter boxes weren't originally manufactured for filtering pond water. Many are useful for mechanical or biological filtration, or both. They are inexpensie and rather resourceful in their own way. Plastic kitchen pot scrubbers, unraveled poly boat rope, plastic pop bottles run through a paper shredder, PVC pipe shaved on a lathe, plastic hair rollers, even little green Army men, all have been pressed into service in the fight to keep pond water clear and clean....so, don't be afraid to use your imagination.

CONSTRUCTING OUR FILTER

When designing our filter, we decided on using lava rock for our media bed for several reasons. Surface area...the more surface area you have, the more bacteria you can grow. Mechanical filtering ability...because lava rock is very porous, it captures a lot of the solid materials, thus making it an excellent mechanical filter. Availability...it can be purchased at any home improvement or garden center for less than $5.00 per cubic foot.
Plastic 55 gallon drums work well for these type of filters. You can use anything from a 5 gallon bucket to a 400+ gallon stock tank, or even an old kitchen sink. We used a 75 gallon galvanized stock tank, purchased from Home Depot. It is a 24"x36" oval tank and 23" high. The basic design will be the same for any of these. Remember that a filter can never be too big. Larger filters result in better overall water quality, which in turn increases your ponds ability to support more fish and will require less maintenance than a smaller filter. Below are step by step instructions on how to build our lava rock filter.

1. Using a saber saw, cut a hole 8" from the bottom of the tank to accommodate your water supply that will be coming from your pump. (Be sure to measure 8" to the top of the hole) The hole needs to be just large enough for a 1 1/4" male threaded coupling to screw into. Apply a bead of aquarium silicone to the threads and secure with either a pvc nut or a female threaded coupling.
Do the same for your discharge and drain, (position your drain as close to the bottom as possible), remember that the water is coming in under pressure and discharging by gravity, so your discharge openings need to be considerably larger. We used four pieces of 1 1/2" pvc pipe which works very well with our 2800 gph pump. If your planning on using a larger pump, you will need larger openings or additional openings for the purpose of preventing overflow.

2. Cut a piece of egg crating, (which is used as a light diffuser for fluorescent lights), the size and shape of the inside of your filter. Cut extra pieces of the crating large enough to cover your water discharge pipes...it can be attached easily by using a hot glue gun, this will prevent leaves and other debris from clogging your pipes and thus causing overflow. Next, you will need 10 to 12 pieces of 1" pvc pipe that is cut 9" long. Drill a small hole approximately 1/2" from one end on each piece. Using stainless steel safety wire, attach each leg to the egg crating so that it will be supported just above your water inlet. This is what will support your lava rock as well as leaving a 9" area for heavy sediments to collect.

3. Position your pump at the opposite end of the pond from your filter. Run the discharge line to the filter, installing a ball valve somewhere in the line. This will keep the heavy sediment from running back into your pond when the pump is turned off for maintenance. A check valve could be used instead, however they are not as reliable and more expensive.

4. Rinse your lava rock thoroughly before adding to your filter. Leave a 2" space between the top of the lava rock and the bottom of the discharge pipes. This will provide a setteling area for the lighter sediments that are known as floc.

5. If your filter is an after thought like ours was, an inexpensive, yet attractive way to conceal your stock tank is to wrap the outside of your tank in cedar pickets. Be sure to buy the dog eared pickets, not the pointed type. This will allow you to get three sections out of each board. Cut all the pieces to length and because there is a lip on the top of the tank, you will need to nail a scrap piece of wood to the bottom of each picket to act as a spacer. To temporarily hold the boards in place, you can use a rope / bungee cord combination wrapped around your tank. Slide your pickets underneath the rope, level your pickets and secure them with galvanized fence wire and turnbuckles.

6. Your filter is now ready for use. The mechanical part of your filter will begin immediately. It will take 6 to 8 weeks for the good bacteria to become established in your media bed. You can speed up this process, by seeding your filter. Simply use a shovel load of lava rock from a friends filter which is already established. Several types of plants will do well in the top of your filter. This will not only provide coverage, but will also aid in the filtering process.

7. Cleaning your filter. How often you clean your filter is based on several factors, such as....its size, how many fish you have, what and how much you feed them and weather conditions. (We clean ours 2 to 3 times a season). To clean, turn off the pump and close the valve on your discharge line from your pump. Open the drain and, using a high pressure nozzle, wash the lava rock until the water runs clear. Regardless of how long you flush the rocks, when you turn your pump back on, it will fill your pond with a cloud of floc. "DON'T PANIC" By the next morning, your pond water will be clear again. The tip of the day is.....Don't clean your filter, two hours before the local Pond Society is coming over to your house to take pictures of your pond.

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