Filtering Your Water Garden

I said in previous posts I would talk about filtration. I'm here to say that it's not as daunting as some may feel after reading about different types of filter systems. I'll also say that there are many ways to filter a pond but most backyard ponds will benefit greatly with the information I am sharing here. I will not be giving advice on what brands of filters, pumps or skimmers or any other commercial product for that matter, those are decisions for you to make based on the information I give you here and the amount of time and money you want to invest in your oasis.

The principle elements to good filtration are, adequate water flow, skimmer, and biofilter for the given quantity of water. The function of the three are. Pump = circulation, Skimmer = home for pump and mechanical filtration. Biofall = home for beneficial bacteria and mechanical filtration. A good estimating tool for figuring out how much water you have in your pond, if you don't already know, is this formula,

Rectangular: Length x Width x Average depth x 7.5 = Volume in gallons
Circle: 1/2 x diameter x 3.14 x Average depth x 7.5 = Volume in gallons
Free form shapes: Break the pond down into a series of rectangles and circles and figure the volume of each area separately, then add the volumes together. Each cubic foot contains 7.5 gallons of water, so multiply the total number of cubic feet times 7.5 to determine the total number of gallons.
These are good tools for ESTIMATING the amount of water you have in your pond. However, there is none better than the water meter to your home. Take a reading from your water meter before you add water to your empty pond and then after its full subtract the first reading from the second, that total will be your number of gallons. This will be the most accurate reading you can get and will remain the same for the life of the pond. Write it down somewhere you won't lose it you will need it for future reference...trust me you will want to have this number when you decide to medicate your fish or treat your pond with any type of algaecide.

Ok you now know approximately or even exactly how much water you have in your pond. Time to choose a pump. The basic rule of thumb is the pump should circulate the entire volume of the pond in two hours. So if you have a pond with 1000 gallons of water you need a minimum pump size of 500 gallons per hour (gph). This number represents the MINIMUM amount of flow. Most waterfalls require much more volume to be aesthetically pleasing so I generally select the pump on the size stream or fall that I would like to see in the setting. The basic formula for that is 1000 gph for six inch width @ 1/4 inch of water over the fall. Again that is an estimate many things depend on how much water traverses the fall you have built. This takes care of circulation, keeping the water moving is the circulatory system of the pond. Pumps come in two basic configurations, internal and external. Internal or submersible pumps are the most common and come in sizes varying from 50 to 15,000 gph. These pumps are very efficient and run 24 hrs a day, 7 days a week and can last several years. External pumps essentially have no limit other than budget and size. These pumps are also quite efficient although because of their size will generally cost more to operate.

Next is the skimmer. There are many skimmers available on the commercial market and I do advocate buying one of these, building one yourself would prove difficult for the amateur ponder. Skimmers are the single most revolutionary development in ponding in the last 20 years. A skimmer is the heart of any well built pond and will save you hours of work each year. The pump lives in the skimmer and it is well protected in this environment. All the particles that would normally be drawn into the pump if it were inside your pond are skimmed out of the water before it gets to the pump. The pump doesn't have to work as hard because it doesn't get clogged with debris, and the pump will last much longer. This is the beginning of the mechanical filtration process and a very important and useful piece of hardware. Most skimmers use a two stage process, right after the water intake is a basket to capture large debris this is removable and easily cleaned. Some skimmers have nets, not as easily removed and cleaned but they do serve the purpose. After the basket or net most skimmers will have a filter mat, this mat is designed to filter out smaller particles and does the job quite well on most skimmers. A filter that works well will need to be cleaned often, especially in a pond with a heavy fish load. It is important that this filter be kept clean because submersible pumps need water to keep cool. If the mat gets full of debris no water can get through and the pump will run dry, a pump that runs dry gets hot and that will drastically reduce the life of any submersible pump.

From the skimmer the water travels to a biofilter. Biofilters have an even wider variety of styles than skimmers do and all of them serve one main purpose, to house and nurture beneficial bacteria. Biofilters are relatively easy to build and even the home made units function quite well, after all your just creating surface area for the bacteria to grow on. Let me take a moment to describe the nitrification cycle. This is a brief description and much study has gone into the understanding of this life cycle. In an established ecosystem, one with fish, plants and good circulation, fish release ammonia, nitrosomonas bacteria consume the ammonia and release nitrite, then nitrobacteria consume the nitrite and release nitrates, nitrates are mostly harmless to fish and feed plants as a form of fertilizer. Ammonias and nitrites are deadly to fish, these chemicals must be converted as soon a possible to the relatively non lethal form of nitrate, thats where the biofilter comes in. The bacteria that perform these conversions will form naturally in a pond and all ponds have them present. However for them to do the job we need to keep our pond healthy the water flowing and give these beneficial bacteria a nice home to live. The beneficial bacteria need surface area to propagate and survive the biofilter provides that surface area by means of media and one more critical element, oxygen. Beneficial bacteria need oxygen, lots of it, it's for this reason that the pump in your pond must run constantly 24/7/ 365 days a year. Water flowing over the bacteria provides the much needed oxygen for the bacteria as well as bringing particles into your filter. A shutdown of more than three hours in the heat of the summer will starve the bacteria of oxygen and kill it. Your filter will not function as intended until the bacteria can re-propogate. A well built biofilter will have a settling chamber, a filtering chamber and a bio-chamber. This type of configuration provides progressively finer filtering and the final chamber is chemical filtering. I will elaborate more on building your own biofilter in future blogs. The first chamber is just as it sounds, a place for particles to settle out of the water flowing through it. Since most particles at this stage of filtration are heavier than water they will settle out in a chamber that slows the flow of water down and allows the settling to occur. In the next chamber some sort of filter material such as mats or brushes filter out the even finer particles that don't settle out in the first chamber. These two chambers are mechanical filtration and in a pond with a heavy fish load will need to be cleaned frequently. The final chamber is where the biological media is kept. Bio-media is anything that has a lot of surface area and there are many commercially available products. Many people use gravel or lava rock and these work adequately but the commercial brands will provide much more surface area as this is what they are designed for.

I would be remiss not to mention that there are other types of filters that can be purchased and built some of which are easy to build and some that can only be purchased. Examples are:

Trickle towers, these are constructed of different size barrels according to the size of your pond. The basic idea is to run water over filter media and let gravity do the work to return the water to the pond.

Bead Filters, Bead filters are manufactured in several different sizes and are quite efficient at removing particles from your water and the beads act as media for beneficial bacteria. These are quite easy to maintain, but can be quite expensive as well.

Underwater Gravel Filters, These filters are based at the bottom of the pond and draw water through a media box. this type of filter is very labor intensive and I do not recommend them for anything but the smallest ponds (under 250 gallons).

Sand Filters, These filters are known by many ponders to be very good at keeping the water very clear and the sand acts as a good media for the beneficial bacteria. These are very similar to pool filters. Drawbacks are that the sand tends to channel the water and reduce the efficiency of the filter. Unclogging them can be a chore and may need to be done quite frequently.

Glass Filter, A glass filter is the same as the sand filter mentioned above with the difference being the media contained in the chamber. A recycled glass product is the basis for the media and this type of media resists the channeling that happens to sand resulting in a more efficient filter and much better cleaning. This type of filter may be cost prohibitive to many, but it will give years of service and clean water.

All of these filters but the first can be purchased and although they all work to a degree of efeciency it has been my experience that a biofilter of adequate size for the given volume of water and flow will work as well as any of these at quite a substantial savings to the ponder.

Now you have some basic information to try to decide what type of filtration system to install in your backyard oasis. I hope this has helped you to make an informed decision. And as always if you have a plan for a pond but are hesitant to implement it please feel free to call on me for advice and consultation.

Doug Coe
Dreamscape Water Gardens
www.dreamscapewatergarden.com